Why don't you try building one of your own? It's damn easy... Power supplies are the electronic projects many students and newbies start with... (Voice of experience)
Building your own would be much much costlier (10A) than buying a dam cheap SMPS for computers. It has 2 outputs 5V@25A and 12V@10A and some has even more voltages.
im for the computer suply 2.....
thing of building your own suply...if u would use a simple transformer, rectifier and a ton of capacitors..and the transformer would be very expensive, not to mention a small eficency......
but building a switching powersuply would be much more complecated so..
if i remember well u could find good computer suplies at 8-10 bux, and they also have other voltages, 5V@15-30A and -5V@5-10A and so on...
Just keep in mind: the older ATPSU regulator feedback only from 5V output,therefore can`t work without 5V load.
When this feedback replace to 12V (with additional serial poti), i can charge a car battery with 15A.