Try plugging your rig into the socket/outlet directly. You may have a bad surge protector or it's designed to shut off at specific loads we have no idea about.

I had the exact same problem a few months back. I tried changing everything from drivers, to risers, to cables, to PSUs. Turns out that the problem was that my extension cord / surge protector for some reason automatically turns itself of. Never would have noticed it until i sat beside it for an hour and saw it right before my eyes, the surge protector's switch simply turned itself off.

I've since them switched to an extension cord without any switches at all. Been running a stable rig ever since.