And there is all sorts of minor hardware and sophisticated (but generally free and open source) software that can turn a PC into a useful lab tool.
Step 1: Lab Power Supply
With slightly more effort, you can add some fuses and ammeters, both of which are probably good ideas.
With significantly more effort, you should be able to come up with a variable voltage current-limited supply that still fits in a bay.
(Picture from http://www.instructables.com/ex/i/2F7340901BE310299AD7001143E7E506/)