Ok, I sent the NeoPowerHE 550 back to newegg, swapped in a Seasonic S12 600W. Machine works fine now, rock solid. No more weird shutdowns.
So definitely stay away from the NeoPower HE until they sort out their problems.
I can confirm the NeoPower HE 550 does not work with my Asus A8N Premium rev 1.02 board. AMD64 x2, 2gigs OCZ Platinum, GF7800GTX. All the power connectors on the motherboard are plugged in (incl the ATX 4 pin aux power and the EZplug). The motherboard has been flashed to the latest on ASUS's...