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All laptops require a AC adapter in order to convert electricity into a usable form for the laptop. In most AC adapters I've seen, the plug is directly connected to the power brick, meaning that the brick is generally extremely close to the socket when plugged in.

I feel as if this is a poor design choice for the following reasons:

  • The brick is heavy, so this causes the plug to sometimes loosen when plugged into a socket, especially when it is a wall socket
  • Due to the size of the brick, the AC adapter tends to block other available sockets

While there are other laptop AC adapters that do have two separate cables that get combined at a transformer brick in the middle, it doesn't seem to be as common anymore. I'm also aware that most AC adapter bricks are modular in that you can swap the plug out for a longer cable.

That said, is there any technical reason, particularly when it comes to hardware and electronics performance, for why AC adapter bricks are placed at the AC plug-end rather than being in the middle by default?

To be clear, I am asking about why many AC adapters look like:

enter image description here

rather than:

enter image description here

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  • \$\begingroup\$ My 2014 Lenovo had a power brick with a cable at each end (LV cable, AC socket), my 2022 Lenovo has a wall wart (small square with plug). I dispute that it's heavy - only 200g - and a decent (BS1303) plug easily holds it securely. \$\endgroup\$
    – user16324
    Jan 3, 2023 at 22:18
  • \$\begingroup\$ IMO, a heavy power brick is safer on the floor than on a desk next to the laptop. It also then doesn't take up valuable desk space. \$\endgroup\$
    – SteveSh
    Jan 3, 2023 at 22:23
  • \$\begingroup\$ why do some cars have the window controls on the doors and some on the center console? why do some have the windshield wiper controls on the left side of the steering wheel and some on the right. various reasons some of which can be size and weight of the transformer. some can be cost of the thicker power cord vs thinner and a longer thinner is cheaper. a lot may be universal solutions with the wall power side using a different cable/plug for the target country. although apple sort of solved that with theirs. end of the day, some engineer or team made a choice for their design... \$\endgroup\$
    – old_timer
    Jan 3, 2023 at 22:32
  • \$\begingroup\$ It makes passing UL and other agencies easier. \$\endgroup\$
    – Kyle B
    Jan 3, 2023 at 23:35
  • \$\begingroup\$ I've never seen an actual laptop with a wall wart. They usually use the cord-on-both-sides type of power supply. \$\endgroup\$
    – Hearth
    Jan 4, 2023 at 1:32

6 Answers 6

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The white 'charger' is a USB C power supply with maximum power output of 60 W. These are typically used with tablets and small laptop computers that use less than 60 W.

Larger laptops and mini desktop PCs generally use a 19 V power supply rated at 65-90 W or higher. Your image matches this 'charger' on Amazon which is rated at 90 W.

The more power a PSU provides, the bigger the electronic components inside it have to be. A USB C power supply is (just) small enough to fit in a case that plugs directly into the mains socket. Not having a power cord means it can be made smaller and cheaper - two things that make it more attractive to the buyer.

However I suspect the main reason for making it this way as that USB power supplies traditionally have done it this way - since they were commonly used with cell phones and other small devices that needed less than 5 W of power. There was little point having a large power cord going into a tiny box when it could just be plugged directly into a mains socket.

However as cellphones got more powerful and USB became a ubiquitous power source, more power was needed. Manufacturers like Apple put much effort into increasing the power density to keep the size down. That wasn't possible with USB C, but they still tried to get it as small as they could.

When you are touting the ultra-thin form factor of your tablet or mini laptop, you don't want to spoil it with a bulky power supply unit that is bigger than the device it is powering! That means no separate power cord, even when the box is so large that it may have difficulty staying in the socket.

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  • \$\begingroup\$ Ah okay, that does sound plausible. Cellphone USB power supplies are small enough that they don't suffer as much from the issue of hogging space and being heavy when connected to an outlet, but modern laptop power supplies such as those for the Macbook or ASUS Zenbook are large enough that I think they should be designed as a more traditional "brick" supply. \$\endgroup\$
    – Feiri
    Jan 4, 2023 at 1:02
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You're actually asking: why do some AC power adapters plug directly into the wall ("wall warts"), while others use a power cord ("bricks")?

First, please understand that they both are power supplies (AC to DC), not transformers (AC to AC). Also, note that they are not "chargers", they are power supplies. The charger is built into the laptop.

To answer your question:

Larger power adapters ("bricks") are too heavy to plug into the wall, so they must use a cord. Smaller ones ("wall warts") are light enough to plug into the wall without falling off.

Regardless, a power adapter may use a cord for ease of adapting to many different countries: it's easier to ship the cord for a given country than it is to change the plug design in a wall wart.

By the way, in case you're wondering why we don't plug in an AC power cord directly to a laptop computer:

Limiting the high voltage to the power supply brick makes it far easier to make a safe laptop computer. Instead of having everything in the entire laptop computer meet safety regulations, only the power supply needs to be tested to regulations about high voltage circuits and only it needs to pass.

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  • \$\begingroup\$ Thanks for clarification on terminology! However, is an AC to DC converter not considered a "transformer?" At least in plain English I'd say that the conversion between AC to DC is considered a type of "transformation," but perhaps it's not a technically accurate term. I'm still left a bit confused on why wall warts exist, as opposed to following the more traditional brick design where you can plug a smaller cord into the wall, then have the brick stay on the floor. The way I see it, wall warts hog a lot of space near the outlet, but detached bricks do not. \$\endgroup\$
    – Feiri
    Jan 4, 2023 at 0:53
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    \$\begingroup\$ No. A transformer is only AC to AC. See: en.wikipedia.org/wiki/Transformer \$\endgroup\$ Jan 4, 2023 at 0:54
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    \$\begingroup\$ @Feiri A transformer is a specific electrical component, at least in English. As I understand it, some other languages use the same word to refer to AC-DC converters, but English does not. \$\endgroup\$
    – Hearth
    Jan 8, 2023 at 15:13
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    \$\begingroup\$ @Feiri Many people call it "a transformer" as it changes voltages, people who know a little bit of electricity call it "a rectifier" since transformer is AC-to-AC only, but a rectifier converts AC to DC. But electronics people understand that "rectifier" is also wrong as it does not convert or regulate voltage. it's really a combination of a rectifier, a transformer, a pulse-width modulator, a low-pass filter, a regulator, etc., so you use the technically most accurate term - just "a power supply." To be fair, pure-transformer power bricks still exist and useful for, e.g. analog audio. \$\endgroup\$ Jan 8, 2023 at 15:17
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My Mac has an 85W power brick which comes with a clip on plug to use directly in a socket (plug is available in several flavours to match sockets around the world) and also comes with a cable of 2m length.

Perhaps other manufacturers are just cheap…

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To be clear, I am asking about why many chargers look like

As usual, the most likely reason is cost: it saves the cost of the power cord. The modular plug is probably as cheap as the IEC connector alone. It also makes the whole thing lighter and smaller, which saves on shipping, stocking, inventory, etc.

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  • \$\begingroup\$ Honestly I was hoping there might be a more technical reason for selling power supplies as wall warts instead of bricks, but this answer does seem pretty straightforward and understandable from a business perspective. \$\endgroup\$
    – Feiri
    Jan 4, 2023 at 1:07
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One thing not mentioned your DC power bricks are expected to rest on the table or floor. That's a pain in itself.

If it's light enough to not need to rest on something, you still don't want that bulk mass in the middle of the cable because now it's a swinging mass. You want it rigidly connected at one end of the cable, and that's not happening at the laptop or phone end.

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Cost. Cost. Cost.

If you conceptually replace the black adapter with the white one, you have to change the AC input plug to a socket and add the cost of the AC power cable to the product. The producing company now is responsible for the safety ratings and high-voltage reliability of two things (the adapter and the AC cable) instead of just one.

Note that the power cable is larger than the adapter body, so the size of the product packaging must increase.

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