How accurate do you need it? What voltages and current?
I have a 450w PC power supply on my bench for doing some of these things.
You get +12, +3.3 and +5 VDC at pretty good amps. the -12 and -5 don't have much oomph.
I wouldn't trust it to calibrate a meter tho. If you really want a meter to be right, you need to send it to a lab.