Tom: I actually built something precisely like that. It's on a plank of melamine, weighs about 20 lbs and provides up to 30VDC (variable) or +/- 30VDC (fixed) that runs on a big toggle switch. The xformer is a mains type that I think is 48 VRMS. It's big and was custom made for me when I first needed something to prototype with.
MarkT: That's cool! I'd sure fork out the dough for that if I could find one that supplies 25V. 5 unfortunately isn't enough but I'll see if I can find a beefier one.