Mac Pro 3,1 made sizzle sound followed by puff of smoke. Power supply?

Earlier today, I suddenly noticed a puff of smoke followed by a shut down on my Early 2008 tower. Opened it up, casually searched for signs of scorching/burns, nothing seen. Rebooted and ran fine for about 5 hours, then unexpectedly, the same thing happened. My guess is a wonky power supply. Anyone else experience such?