Mac will not power on. How to test for bad power supply?

Left the mac running last night while it was bouncing down a fairly large audio file. When I checked in the a.m. it had shut down by itself. Re started and the bounced file appeared as if it had completed, there was a folder on the desktop for it. Returned to the Mac about an hour later and it had shut itself off again.

Now it will not start. Light goes on momentarily then makes a plink sound and goes dark like a breaker is shuting it off. I tried to reset the SMU switch on the board with no results.

I have never had a power supply go bad but I'm guessing this is a possibility. Can anyone tell me how to test a bad supply or have experience with this type issue?