Inside your PSU @ Dan's Data

[Steve]

Do you know what goes on inside your computers power supply, or as far as you're concerned is it just "bits and stuff!" Be enlightened by Dan.

The simplest kind of power supply that takes mains alternating current (AC) and outputs low voltage direct current (DC) is the "linear" type, consisting of a transformer, a rectifier, and some capacitors, plus an optional regulator if you don't want its output voltage to vary much with load. Linear PSUs are big and heavy and inefficient, though; about four-tenths of the power going into one leaves as heat, not as useful output. Run a 300 watt stacked PC from a linear supply and you'll have to get rid of at least 200 watts of heat from the power supply alone.

[The article]