washingmachine7 :
That's a generic overrated PSU ...
A 900 watt power supply with 1 PCIe power connector and about 45 amps on the 12 volt rails? What you have there is a 600 watt PSU for all practical purposes.
A 6950 needs about 15 amps at 12 volts and two PCIe power plugs. I think you only have 4 molex connectors and you would need to use two for a molex to PCIe power adapter.
So you have enough power capacity, but you do not have enough cables. And it is a low quality, obsolete design. I say "obsolete" becuase of the power capacity. It has relatively heavy 5 and 3.3 volt rails and relatively light 12 volt rails. Modern systems use 12 volts for all the high powered components (CPU and GPU). A good example is the 850 watt Corsair TX850. It has a 70 amp 12 volt rail.