http://www.tomshardware.com/answers/id-2311121/power-supply-requirements-nvidia-gpus.html#14243229
http://www.geforce.com/hardware/desktop-gpus/geforce-gtx-960/specifications
960 Thermal and Power Specs:
98 C = Maximum GPU Tempurature (in C)
120 W = Graphics Card Power (W)
400 W = Minimum Recommended System Power (W)
1x 6-pins = Supplementary Power Connectors
http://www.guru3d.com/articles_pages/msi_geforce_gtx_960_gaming_oc_review,7.html
Subjective obtained GPU power consumption = ~ 127 Watts
Here is Guru3D's power supply recommendation:
GeForce GTX 960 - On your average system the card requires you to have a 400 ~ 450 Watt power supply unit.
If you are going to overclock your GPU or processor, then we do recommend you purchase something with some more stamina.
NEVER choose a PSU by brand name.
1. While there are very many PSU suppliers, very few of them actually make a PSU and instead buyt from OEMs.
2. Just about every PSU manufacturer / vendor makes some excellent units, some good units and some really crappy units.
Generaly ....
Corsair AXi, HXi, HX, AX - very good but way overpriced, Rxi very good.... EN, CX VS, etc... don't waste your time.
EVGA - P2, G2 excellent ... B2 GS very good .... B, B1, don't bother
Seasonic - X and Snow series are my fav's .... S12 / M12 are great.
A S12 / M12 520 is 120 watts more than you need.... so plenty for overclocking. The EVGA B2 750 can usually be found for $48 and will handle two 960s. And the Seasonic S12 / M12 620 are sometoimes cheaper than the 520.