system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do some devices need huge, clunky transformers to go from AC to DC, while others (like USB) are just a tiny plug?
gpt
Transforming power from AC to DC is a relatively simple task if you only need a little bit of power.  However, if you need lots of power then you start worrying about the amount of heat that you are producing.

Something like a USB plug is not going to have to supply more than a few watts.  Such a device is never going to have to worry about how much heat it produces.  However, something like a laptop power brick can provide over 100 W (mine is 135 W).  The more power a device needs to draw the more power it has to waste as heat, generally.