Recommend 850, tier 2 PSU:
Ref:
Measured power consumption one card
1.System in IDLE = 144W
2.System Wattage with GPU in FULL Stress = 307W
3.Difference (GPU load) = 163W
4.Add average IDLE wattage ~10W
5.Subjective obtained GPU power consumption = ~ 173 Watts
Measured power consumption two cards in SLI
1.System in IDLE = 155W
2.System Wattage with GPU in FULL Stress = 473W
3.Difference (GPU load) = 318W
4.Add average IDLE wattage ~20W
5.Subjective obtained GPU power consumption = ~ 338 Watts
From:
http://www.guru3d.com/articles_pages/geforce_gtx_680_sl...
Link to Tier List:
http://www.eggxpert.com/forums/thread/323050.aspx
PS: The references to recommended PSU's are based on "lower end" PSUs.