Built one of the ubiquitous ‘Desktop Power Supply’ from a recycled, ATX-form, PC power Supply. Actually used it occasionally to power a 12V charger in the garage. Unfortunately, it fizzled an electrolytic capacitor and it’s really not worth reparing.
So, I rescued all my hardware and built a reusable adapter for ANY standard ATX power supply.
1 ATX Power extender – this is an extension to the wide plug that goes to the motherboard, usually about 9 inches or so (like this one: http://www.directron.com/atxextension.html).
All of the other hardware bits needed to alter an ATX supply for desktop use (binding posts, a switch, a 10 ohm / 15 watt resistor (I used a Dale, metal-cased).
And an enclosure – a wide, thin, Radio Shack enclosure I had on hand.
The 10 ohm 15 watt resistor goes from the +5V rail to Ground. This is needed so that the supply can sense a load – otherwise, it will not start.
Excellent how-to’s everywhere on the net, but this one is great: http://web2.murraystate.edu/andy.batts/ps/powersupply.htm
Great current ratings here: http://web2.murraystate.edu/andy.batts/ps/PowerRatings.htm. The +5 and +12 rails can supply a good deal of power and these ATX switcher supplies are very efficient.