Until now I've used my own homemade power supplies which were not particularly powerful. I just bought a used IG Precision Gp-503 (I haven't got it yet) whose specifications state that it will do 0-50 volts dc and the output current (which is limitable) goes from 0-3 amps. My question is: Can I use this to power a circuit with 50 volts at 3 amps? That's 150 watts!

 

I think you meant LG Precision. They are now EZ Digital.

The GP-503 is rated for 150W, which matches your requirement.

However, if you want to be able to power your 50V 3A circuit indefinitely, you might wish to have another supply available for other purposes.
MPJA.com has these 24v 4.2A (100W) supplies on sale for $10 each:
http://www.mpja.com/email/11-10-09a.asp?r=%%ref%%&s=4
You could wire a pair of them in series after adjusting them to output 25v (there's a 10% adjustment range).

 

Thanks, Sgt! The supply just came to my door via Fed Express. It's heavy and well-built. I ordered it from a seller on E-bay. It sure looks like it can handle 150 watts. I'm excited. Gotta go test it.....