I'm not sure what you mean by quite limited. But IMO that's a great find for $20 and those are very useful PSUs, particularly with OP amp circuits where you need multiple voltages and +/- voltages. And being made by HP, they're built to last forever and you can get FULL service information and all of the parts for them. The only downside to them is that they're transformer based so they are bigger and heavier than the switcher type PSUs but that also means that there is a lot less electrical noise in the outputs and less radiated RF noise.
What's the date code on that PSU?
FYI, the caps used by HP seem to hold up very well so don't go in there and just start randomly replacing capacitors!