Are you trying to use multi-rail PSUs? My guess is yes. Use a good quality, Gold or Platinum single rail PSU for all mining rigs. Seasonic, Corsair and EVGA make the best PSUs for mining in my opinion.
I have to throw a shout-out for XFX supplies. They're priced well, single rail, and the higher output units are made by Seasonic.
i'm a great fan of the corsair 1200i's i get all jelly-legged when i play with their UI
