Just wondering cus like wouldn’t it be more convenient to just plug your phone into the wall without a brick, or like cheaper to build a pc without a power supply? why do these devices need DC but lamps, fridges, fans, most household appliances can run off AC?
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If you wanted to plug your phone into the wall “without a brick”, your phone would have to include the electronics that are inside the brick inside the phone itself. This means your phone would be 20% bigger, and that 20% biggerness would be with you all the time, even if you only need them for a couple of hours when you charge your battery.
If you tried to put the electricity from your wall directly into a piece of electronics without going through a power supply, the device would in the best case stop functioning, in the worst case literally catch on fire. The circuits that make these devices function are too delicate to be able to handle the much high voltages that the power grid operates on, and the circuits would literally disintegrate from the very high temperatures that would be caused by squeezing a very high voltage through a very very *very* thin wire.
Typically speaking, the thinner a wire is, the less electricity can pass through it. The wires in a computer chip are so thin that you can’t even see them with a magnifying glass, so the amount of power that can fit through them is very little.
You might ask why this is fine in a light bulb, as that’s also a very thin wire but still hooked up to mains voltage. Well, old-school lightbulbs are made from tungsten, which is a very heat-resistant metal. You can’t really make electronics from this material because it’s not a semiconductor. Furthermore, this wire is encased in an oxygen-free gas, which means even if it gets hot, it can’t burn up because there’s no oxygen available to burn in. Had the light bulb not had this, the glowing wire would burn up in less than a second. Also, that tungsten wire in a light bulb is still over a thousand times thicker than the wires inside in a computer chip.
Why they want DC instead of AC is a completely different topic. Whether you want to run a digital or an analog system, you want the input voltage to be stable. AC means the intensity of the electricity goes up and down 60 times (in some regions, 50 in other) a second, and this will severely interfere with the work that the circuit is trying to do. For example, if you have an analog speaker amplifier and some of the mains voltage gets into places it’s not supposed to be, you might get a 60 hz humming in the speakers, which wouldn’t sound very nice.
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