What sort of voltage and current range are you looking for?

What I think you need is something like an ordinary lab bench supply. These often come up on ebay for a reasonable price.

Alternatively you can build one easily enough. I have three or four variable voltage bench supplies that I've built, the most recent being one to power my home made capacitive discharge battery tab resistance welding machine (see pic below - it's the silver box on the left with the digital voltage readout).



Jeremy