My Prusa is currently using an old (and I think slowly dying) ATX PSU. I had a rummage around work's WEEE skip the other day and came away with an HP ESP113 series server power supply (specifically a PS-3381-1C1). It is rated to 32A at 12V and so ought to provide enough juice for the future heated bed and then some.
I followed a guide I found on an R/C forum to make it work (
link here). Putting a meter across the modified supply showed a steady 12.25 volts, so it looks good.
Will try it on my machine when it comes back from it's christmas holidays in the garage.
Just wanted to share as the conversion was fairly easy, there is no need to load up a 5V line for peak output and these PSU's are available on ebay for around £10.
(Photos:
1 2 3 4)