It has been nearly universally the case that the cable which connects an external power adapter (power supply) to a laptop computer is permanently fixed to the power adapter. This makes the cable more or less un-replaceable. Being so, if/when the cable fails, an entirely new power adapter must be purchased.

This is in contrast with phone chargers, which, at least for Android type phones, almost universally have a detachable, and hence replaceable, USB cable between the power supply and the phone.

In my experience, lap-top power cables fail far more frequently than the power supply itself. Having a power supply with a detachable cable that could be purchased separately would seem to be something that would reduce the total cost of ownership for end users, even if the initial cost might be more.

A possible explanation might be that the manufacturers make good money on replacement power supplies, and are relatively unconcerned with the total cost of ownership for the end-user. But that would not explain the absence of such products in the replacement market.

It has made me wonder whether there is some (perhaps not very well considered) regulatory obstacles for the heftier power supplies for lap-top computers that do not apply to the smaller phone chargers. It occurs to me that there may be safety or EMI regulations that make detachable cables for larger power supplies problematic. However, I find it hard to believe that a male or female connector physically integrated in a power supply would pose any more "danger" or EMI issue than the same connector on the end of a cable.

My question is, are there any regulatory reasons or possibly technical problems that militate against a "USB cable" type model for lap-top computer power supplies? (Obviously, USB itself will frequently, not be up to the task in terms of power.) Or, is the lack of lap-top power supplies with detachable cables on the low voltage side merely the result of suppliers having little incentive to reduce total cost of ownership?

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    \$\begingroup\$ My Dell USB-C power adapter is rated at 60 W. Whatever is connected can negociate for 5 V, 9 V, 15 V, or 20 V. All 3 A max. I assume that the laptop is asking for 20 V. \$\endgroup\$
    – Mattman944
    Sep 15, 2023 at 23:31
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    \$\begingroup\$ @MathKeepsMeBusy The USB-C connector (same form as the thunderbolt 3 and 4) seems to me to be growing in popularity. (I'm certainly encountering it more often than I recall a few years back.) The Thunderbolt cables are rated for (6) separate 15W devices or one 100W device. So says my Lenovo docking station, anyway. But I think it is just a few nickels cheaper to do without another connector on the brick. I'm also not happy, because I have a very young, very large Pyrenees that loves to chew up cables he can reach (which is anything lower than 6 feet above the ground. ;) Shetland pony sized. \$\endgroup\$ Sep 15, 2023 at 23:37
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    \$\begingroup\$ @MathKeepsMeBusy The right to repair movement might have some impact, someday, on this. No idea if or when, though. \$\endgroup\$ Sep 15, 2023 at 23:41
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    \$\begingroup\$ Until USB came along, all phone adapters had fixed cables. It just makes them cheaper to make. And there are probably none in the replacement market because people generally want a replacement that looks just the same as the original. Personally, it's just one more item to lose. \$\endgroup\$
    – Finbarr
    Sep 15, 2023 at 23:57
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    \$\begingroup\$ As mentioned, USB-C laptops up to 100 W is now commonplace. Laptops with Thunderbolt 4 certification must be able to charge via USB-C. I have a Lenovo USFF desktop that can be powered via USB-C. USB PD 3.1 (2021) extends this up to 240 W, this is just starting to come on the market. \$\endgroup\$
    – user71659
    Sep 16, 2023 at 2:00

1 Answer 1


There are four different approaches/paradigms currently in use.

Standard port, conversion circuitry on the device.

This is the method chosen by modern cell phones and by AC charging on EVs.

Cell phone power draws are very small. As such, it's not hard to use a standard voltage (e.g. 5 volt USB) and do the necessary conversion right on the phone.

EVs, for the sake of system architecture, do low speed (1-22 kW) charging via an AC power connection. They accept run-of-the- mill, "right out of the wall" 100-240V into their Tesla (J3400), Fetch (J1772) or Mennekes (J3068) charge ports. Onboard the car is the battery charger proper, the size of a suitcase and water cooled.

This is hard. It adds a 50-100 pound module, cabling, contactors and coolant to every car. if it wasn't done, things would be much messier. People would be supplied a home literal charger that could only charge the 2nd generation Nissan Leaf. They would have to carry it in their trunk everywhere so they could charge when available.

Constrain the design of everything

This is the approach used on golf carts. At a golf course, every charger can charge every make of cart, because they are all 36 volt wet lead-acid architecture. Downside: the design of golf carts is constrained to 36 volt lead-acid batteries. That was fine up until about 2015. Now with lithium ascending, it's a mess.

All singing, all dancing Super Charger

This keeps the simplicity in the device, but requires great sophistication in the charging equipment. This is being done with the USB charging standards (able to deliver up to 100W), and the DC fast charging scheme for electric vehicles.

The device must handshake with the Super Charger, and negotiate a charging plan, particularly pertaining to battery voltage and max current. (So you aren't pushing 200 kW into a Chevy Bolt whose battery cooling isn't good enough for that). The Super Charger then needs to have the sophistication to output that voltage and current, because it is attached directly to the battery terminals. A module on the device supervises and makes sure charging is going well.

But of course even this has limits, e.g. the inability of USB to charge larger, higher-power laptops... and 500V Tesla Superchargers' inability to deal with 800V architecture platforms like Porsche Taycan, Hyundai Ioniq, etc. Those cars have onboard step-ups, but their capacity is limited.

Custom power supply for every device

In this case the charger is closely matched to the requirements of the machine's battery, so only de minimus charging electronics actually needs to be on board the device.

This is what most tools, razors, pre-USB cell phones and older and large laptops do.

Some effort is made to make the charge ports different enough that it's hard to plug a laptop into a charger which would damage it.

This is where you're at. You want easily replaced cords, but every cord will be different, so you'd need to mail order that cord from a limited choice of suppliers. And that wouldn't work any better.

So what you're really saying is that you want laptops (not already on USB) to have a universal/standard adoption of one of the three options I listed above - onboard charge equipment (making it bulkier and heavier), all laptops use the same battery architecture, or all laptop chargers are Super Chargers.

Larger and older laptop power supplies are a custom match to the laptop's battery.

Your paradigm is coming out of cell phones and tablets, where they take the standard USB power supply of 5 volts and adapt that to the phon

  • \$\begingroup\$ What pre-USB cell phones put the battery charger outside the phone? I had thought most of those used USB or something very similar but with a custom connector--I know I had a Nokia flip phone in the mid-00s that came with a USB-to-whatever-the-phone-used cable for putting ringtones on and it and stuff. \$\endgroup\$
    – Hearth
    Sep 17, 2023 at 0:17
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    \$\begingroup\$ Also, almost all laptops do take the same supply voltage of 19 to 20 V. So I don't think your argument at the end is really quite valid; the laptop "charger" is just a 19 (or 19.5 or 20) V power supply, and all the charging and battery management is on the laptop. Since that's also true for a lot of the other things you list as using your last system, I'm wondering if I misunderstood your argument.... \$\endgroup\$
    – Hearth
    Sep 17, 2023 at 0:20
  • \$\begingroup\$ @Hearth The coincidence of near voltages is not proof of genericness. As long as power supplies are designed to serve particular laptops, they can offload as much of the charge control circuitry as they want into the external power supply. There are several species and sizes of lithium battery and they have different charge characteristics. Just because one wishes a thing was done doesn't mean it's been done. But if you want it to happen, head to Brussels - they seem most responsive to this type of thing. \$\endgroup\$ Sep 18, 2023 at 17:54
  • \$\begingroup\$ There's also the matter of power - even if voltage was standardized by government edict, a manufacturer of a 130W laptop does not want to ship a 300W power supply with it. So now we'd need to implement a J1772/Mennekes-style approach where the laptop's onboard charger must obey a capacity signal from the power supply. (to be clear, that doesn't "just happen" - normally if you put a load capable of drawing 300W on a 130W supply, it simply overdraws and crowbars the power supply.) \$\endgroup\$ Sep 18, 2023 at 17:58

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