EE Experience: apprentice


There are two devices: Main device #1 contains a 12V DC (2.1A) pump powered by an AC 100/240V to DC 12V (10A) main power supply; secondary device #2 contains a 5V DC (2.1A) LED strip and a 12V DC to 5V DC buck converter. Device #1 will provide power to device #2 via an 8" detachable 2 conductor 20 AWG cable with tinned copper strands.

Question: What is the best (most practical) way to do this?

My first thought is to use an 8" male to male cable.

And use two female panel mount DC connectors.

Note: those Digikey connectors are listed under "power connectors" which leads me to believe that they can be used either as a powered (provide power) or a non-powered (receive power) connector in contrast to typical usage whereby the female jack/socket is almost always used in a device to receive power via it's corresponding male plug.

As I'm looking at both the standard DC male barrel plug and female barrel jack/socket, it looks like a human finger has about the same chance of touching the positive center pin (in my case) on either the male or female DC barrel plug which leads a novice such as myself to believe that I can use the female jack/socket to provide power.

IMPORATNT UPDATE! I spoke with Digikey tech support. They said in contrast to popular belief, a DC barrel jack/socket can in fact be used to provide power in contrast to its typical usage to receive power; the reason we see devices using the barrel jack/socket to receive power is for design preference because the female barrel jack/socket is flush with the surface of the device in contrast to the male barrel jack plug.

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    \$\begingroup\$ For what it's worth, Digi-Key refers to the "jack" (with a pin inside of a large socket, usually part of a device) as male and the "plug" (with a small receptacle inside of a "barrel," usually part of a cable) as female. The words "male" and "female" are usually applied based on the smallest contact, which is the center pin, so the connector bearing the center pin is designated as male, and the connector that accepts the center pin is designated as female. With all that being said, maybe it would be clearest to always describe barrel connectors as "plug" and "jack," not "female" and "male." \$\endgroup\$ Commented Sep 9, 2023 at 13:28
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    \$\begingroup\$ A metal contact is a metal contact. On some dc devices (I know of power banks, and solar charge controllers), barrel jacks are the connectors used at both ends. USB OTG (and more recently USB C) are not barrel but use the same port regardless of direction of current. \$\endgroup\$
    – Abel
    Commented Sep 9, 2023 at 16:18
  • \$\begingroup\$ Very good analogy. It makes more sense when thinking about those comparisons you mentioned. It appears that in regards to barrel connectors, the misunderstanding with the majority of engineers is because the typical usage of barrel connectors was accepted as the standard when in fact it's not, as @JYelton wisely pointed out. \$\endgroup\$
    – tayglo
    Commented Sep 9, 2023 at 16:33
  • \$\begingroup\$ @CassieSwett sensible people refer to the one that goes inside the other as male, by analogy with animal mating... with a connector like DE-9 it's ambiguous which side is "going inside" the other, but there should not be any such doubt with a barrel connector. I hate whoever decided it should be based on the smallest contact. \$\endgroup\$ Commented Sep 15, 2023 at 10:20

3 Answers 3


I'm confused by your question. What do you mean by "without power" in one instance and then "with power" in another? (Do you mean "providing" and "receiving" power?)

You say you have a "12 VDC panel mount outlet": from what? Do you have a power supply with a female DC jack for output? Although unusual, that configuration is often found in, for example, guitar pedal power supplies where a male-to-male plug cable is used to connect between the supply and the pedal. (Those are typically 9 V DC.)

Later on, you mention two things that I think need clarification:

  • The chance of touching the positive center pin with a finger
  • That female connectors are typically used as 'non-powered' connectors

Both of these statements betray some possible misconceptions.

Barrel jack usage

Barrel jacks are frequently used as DC power connectors, so much so that they are often called "DC barrel jacks." There's no rules or standards that dictate what these connectors can be used for, so you might encounter one that is used for data or something else, but it would be somewhat unusual.

Generally speaking, power supplies (wall warts, desktop adapters, etc.) have male plugs while devices have female jacks. But as I mentioned earlier, that certainly is not a standard.

When repairing or replacing existing supplies/connectors, you have to be diligent and consider polarity, voltage, pin and outer diameter, etc. (More details here.) If you are designing from scratch, the voltage, polarity, and diameter of these connectors are completely up to you.

Low voltage/safety

Although DC barrel jacks are designed so that the middle pin is tucked away "safely" this is by no means primarily a safety consideration. In many cases it is merely a convenience for aligning the connector, or to connect ground before positive. (Though since opposite polarity is a thing, that's not necessarily a reason.)

With voltages under ~48 V you needn't worry much about the possibility of touching the positive pin.* If this consideration is driving some of your design choices, you may want to move it to the "don't worry about it" column.


Without knowing more about your power supply, it's difficult to say what the most practical way of connecting your LED strip is. Based on your question, you mention adding a buck converter to achieve 5 V. That suggests to me the most practical way might be to change the power supply altogether, and get one that supplies 5 V with a male plug of the correct size and polarity.

Failing that, a male-to-male cable should work just fine. Just ensure that everything can support the current draw of the LED strip (supply, wires, connectors, and buck converter).

*These low voltages are at little risk of giving you an electric shock, but if you try hard enough you can make anything dangerous.

  • \$\begingroup\$ I am using this power supply: amazon.com/gp/product/B07MXXXBV8 The said AC/DC main power cord will power a 12 VDC (2.1 A) air pump and also a 12 VDC (10 A) panel mount female DC power outlet in device #1. It will also power a 5 VDC (2.1 A) LED strip located in a separate device #2. Device #1 is connected to device #2 via a detachable 8" DC secondary power cable. I chose to place the 12 VDC to 5 VDC buck/converter in device #2 (downstream of the 12 VDC inlet, @ the LED strip) in case someone accidentally plugs the main power cable into device #2 to prevent blowing the LED \$\endgroup\$
    – tayglo
    Commented Sep 8, 2023 at 23:16
  • \$\begingroup\$ Clarification: so there are two 12 VDC inlets: one on device #1 and one on device #2. And, one 12 VDC outlet on device #1. \$\endgroup\$
    – tayglo
    Commented Sep 8, 2023 at 23:18
  • \$\begingroup\$ Clarification: The reason I posted my question here is...I have been told to never have a female DC barrel connector provide power as it should only receive power. And, only to only use a DC male barrel jack to provide the power i.e., a laptop or the majority of small electronics whereby the male barrel jack has to be plugged into a female connector to power it. \$\endgroup\$
    – tayglo
    Commented Sep 8, 2023 at 23:44
  • \$\begingroup\$ And that's because someone will be plugging two power sources together that way. \$\endgroup\$
    – MiNiMe
    Commented Sep 9, 2023 at 7:28

Sure you can use but if you think it why it might be a bad idea you don't really want to.

Because most power producing devices already have plugs and power consuming devices have sockets, that's the current de facto usage and infrastructure you live in.

If you do make a socket as an outlet, it allows you to make incorrect connections and damage something.

If you connect the power supply to your inlet because the connectors are near each other, will it damage something? If you accidentally plug in incorrect plug and you parallel two power supplies, will they damage?

Also there are not that many cables wth DC plugs on both ends that you can buy. That's because usually you don't have the need to connect two devices together from their sockets.

It isn't that mind-boggling at all. And we have many questions if it is a good idea to use standard connector X for custom purpose Y, and most of the time it isn't.

You can use any connector in any way you want, there is no rule or law against it, except common sense to limit use to the de facto usage.

If you use the DC jack to provide power, it allows accidentally damaging something.

Much like you decided it is a good idea to transfer mains power to a bike shed with a cable that has mains plugs on both ends.

Same goes for using USB connectors for non-USB usage. Not a good idea. You or someone else will damage a standard USB device like PC or mobile phone if accidentally plugged in, just because a matching cable looks to be free to use for charging.

There are already too many different and incompatible uses for connectors like 8P8C modular jacks (some people call them RJ45), XLR connectors, TRS plugs and jacks, DIN connectors, D-Sub connectors etc. You can't expect devices to work or even survive without damage when plugged in, even if they have matching connectors.

There are many standards that have mandated which connector to use and how. Some standards (like DMX512, AES/EBU, MIDI, RS-232) have defined to use existing connectors used also for other purposes. Some standards define their own connector (USB, HDMI, DisplayPort) that have not been previously used for any purposes, which guarantees they are used by engineers as per the standard, and there is the assumption it is not used incorrectly to incompatible non-standard purposes.

Some receptacles like HDMI and DisplayPort are identical on monitors and PCs, and the assumption is, you will use a cable with identical plugs on both ends to connect a monitor to a PC, as you would know from the context that it makes no sense to connect two monitors or two PCs together even if the connectors allow it, and the interfaces are designed to not damage if accidentally connected incorrectly.

With USB Type-A and Type-B, standard mandates what kind of connectors are used on hosts and devices, and what kind of cables are defined to be used between them. So as hosts have Type-A sockets and devices have Type-B sockets, you know you only need cables with Type-A plug and Type-B plugs, and it alone prevents from making invalid connections that do damage, as you have no cables to connect two hosts or two devices together.

USB Type-C is different. All your devices have same receptacle, much like HDMI or DisplayPort. Cables can have same Type-C plug on both ends. The standard requires that even before power or data wires are activated on the receptacle, the devices must negotiate their power and data role. For example you can plug in two laptops together, but likely it makes no sense during the negotiation process and nothing happens. Some laptops may allow to start charging the other laptop. But any invalid combination or unsupported role on a device will just do nothing.

That does not apply to your DC plug. 99.99% of the devices are built with the assumption plugs provide power into a receptacle, and cables with plugs on both ends are not needed for that reason.

DC plugs are already a hazard as same plug and receptacle is used for different incompatible voltages and currents. It's already a pain to make sure you are not plugging in a 12V supply into a 5V device, or 12V supply into a 12V device which expects different DC polarity.

So while you can use a receptacle to output power, nobody expects it, and there is no existing infrastructure to support that, such as cables with DC plugs on both ends.

  • \$\begingroup\$ My laptop has 3 USB-C ports (sockets); all 3 ports provide and receive power. Damage to components is more of a device design issue and his little to do with whether or not a DC barrel socket should receive/provide power just like the USB-C ports on a laptop. You make my case, that it is "mind-boggling" because the majority of engineers think like you and @vu2nan which limits design possibilities. Yes, one would hope the device would be properly designed, just like laptops, whereby damage doesn't occur if the plug is inserted into any of the USB-C ports. But that doesn't change the facts. \$\endgroup\$
    – tayglo
    Commented Sep 9, 2023 at 18:19
  • \$\begingroup\$ I would think you would not want to narrow design possibilities (limit the use of a port/jack in direct contrast to what it is designed for) to make up for the engineer who lacks knowledge in proper device design. You would typically cite the correct usage of the component and force the design engineer to meet the device design standard for that component. If he/she wants to use a connector to receive/provide power, so long as the connector is used in accordance with the manufacturers specs (which in my case it is), one would think that should be perfectly fine. \$\endgroup\$
    – tayglo
    Commented Sep 9, 2023 at 18:33
  • \$\begingroup\$ @tayglo Aha, but Type-C is different, you can't possibly bring it up and compare it to a measly DC plug! It is mandated by a standard how it must operate and how connecting any device to any other device must not result into damage, and the devices must negotiate their role for data and power, before even connecting power or data to the connector pins! Even Type-A and Type-B are more comparable to a DC plug. You can't have an USB cable with two Type-A plugs, as it is not a sensible thing to do, to allow two power-sourcing host devices to be connected together. \$\endgroup\$
    – Justme
    Commented Sep 9, 2023 at 19:16
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    \$\begingroup\$ @tayglo No there is no misunderstanding here. We all know that connectors are just electromechanical devices which can be used for any purpose and in any direction and there is no rule or limitation that you can't use DC sockets to provide power to a plug, i.e. in reverse to what it is commonly used, unless it is a very special case. Such as festive lights that already have a cable towards the power supply, they can have a DC plug, and the power supply has a DC jack eceptacle. Or multi-port supply for guitar pedals. It's already been done. \$\endgroup\$
    – Justme
    Commented Sep 9, 2023 at 21:55
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    \$\begingroup\$ @tayglo I must also point out that your statement that "there seems to be a misunderstanding with the overwhelming majority of engineers, such as yourself" seems very arrogant. If you find yourself in a situation where you believe one thing, and the overwhelming majority of engineers believe a different thing, you should assume that it is you who has misunderstood something. \$\endgroup\$ Commented Sep 13, 2023 at 3:46

In general, electrical power connectors are designated as 'male' and 'female'.

The terms 'plug' and 'socket' are also used instead of 'male' and 'female' respectively.

The female connector or socket is a receptacle that receives and holds the male plug.

Here's a barrel plug on a cable that plugs into the PCB-mounted barrel socket, shown alongside, enter image description here enter image description here

or into the barrel socket on a cable, shown below.

enter image description here

It is standard practice to have the barrel plug feed power from the source to the barrel socket on the device.

This ensures safety and proper functionality and prevents unsafe or non-functional configurations that could result in interconnection of two power sources or two devices.

Image Credits:

Emerging Technologies
Quartz Components

  • \$\begingroup\$ Please see my "Important Update" in my main post. Assuming the Digikey tech and @JYelton are correct, it appears that you and I (and the majority of engineers) had the same misunderstanding in that just because DC barrel jacks/sockets are typically used to receive power that they shouldn't be used to provide power. This seems to be a major misunderstanding and probably needs more scrutiny because it's mind-boggling that this seems to be the first time this subject has been addressed. \$\endgroup\$
    – tayglo
    Commented Sep 9, 2023 at 16:23
  • \$\begingroup\$ I have gone through your 'important update'. My response to that would be identical to what @Justme has elaborated in the first three paragraph's of his answer. \$\endgroup\$
    – vu2nan
    Commented Sep 9, 2023 at 17:50
  • \$\begingroup\$ See my response under @Justme answer. \$\endgroup\$
    – tayglo
    Commented Sep 9, 2023 at 18:36

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