system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: Why do some things (e.g. Laptops) need massive power bricks, while other high power appliances (kettles, hairdryers) don't?
gpt
Electricity comes in two flavors: spicy (AC) and bland (DC). There's also two other things that are important: how fast do you want it coming in (voltage) and how much do you need (amps).

When you plug into a wall outlet you're getting Spicy AC power at 120 volts in America or 230 volts in Europe and a standard house circuit can supply 20 amps (at least in America, not sure about other places). In either case that's the electrical equivalent of having your garden hose on full blast, it's coming out pretty good but it's still relatively safe and usable for the average person. For big dumb things like a hairdryer or a blender that just want to go fast or get hot this is great. Just take that full blast spicy power and go brrrrrr. Similarly you could hook that full blast hose up to your lawn sprinkler and it'll work fine.

If you want to run something a little more sophisticated though like a laptop or a Playstation you need that bland DC power. AC power is all wiggly, DC plods along in a nice straight line and if you want to do math with electricity it needs to move straight. You also probably don't want it coming in so full blast. Your sprinkler may be able to handle the hose on full, but if you stuck it in your mouth you'd probably have a problem pretty quickly. So you gotta turn the spicy AC into bland DC, that's what the power brick does. You also need to turn the hose down, it also does that and brings the voltage down from 120 or 230 to usually something like 5-12 depending on what you're running. Instead of your hose on full it's your faucet on at a trickle.

I also mentioned amps earlier, basically how much power do you need. Keeping with the hose analogy how big a hose do you need? Your house circuit can supply up to 20 but you've got to filter that through the transformer in the power brick.. If you're just charging your cell phone you don't need much at all so the dinky little block that fits in your hand is fine. If you want to run an Xbox though you'll need more. All that math requires a lot of power, so you gotta have that much larger brick to get the same bland 5 volts, but you need 2 or 3 amps worth and you need more space to accommodate the hardware for the additional capacity.