MoneyMorpheus, thanks for the help.

The 1st PSU isn't dead, it's the 2nd one that turns off! All my cards are running at ~75C so that shouldn't be a problem. I'd LOVE to undervolt these cards but it seems none of them are reacting to my undervolt settings? I tried Afterburner, Trixx and in cgminer with no visible change in voltage within cgminer!?

Maybe I'm doing it incorrectly. I'll try again today with all those apps and see if I have better luck, and I'm also going to try and measure how much one GPU draws at the current settings and get back to you.

Also, MoneyMorpheus, how do you explain the more powerful 1020W PSU also turning off with three 280x cards?! It should be more than adequate!

I just woke up to other rigs starting to turn off...sigh.