Any PC uses one. I don't suggest you poke around in one without EXTREME care, the input C's charge to over 400V and they hold lethal charges.

I had an idiot friend who started building one at random, blowing up his input transistors, melting his inductors (honest) Please DON'T build one without a lot of study. There are of course low voltage switchers that people like national semoi or maxim or linear tech supply if you want to try them out. Stay off mains switchers !!!

Steve