Well, if the voltages are stable when checked the right way, then the possible failures shift to the primary circuit, it could be a failing inrush protection. You're not pulling more than 400w from that unit, so if a replacement is needed then you could save quite a bit buying a lower specced PSU.
Have you tried unplugging the AC from the PSU for 20-30 seconds before starting it up? That could clear any set triggers on the protection circuits, I occasionally have to do that.
Edit: It's late, and I need sleep, so I won't make any firm pronouncements until Tator or Phaedrus has had a chance to ponder your situation.
Edited by allikat - 2/24/11 at 10:01am