For a system using two GeForce GTX 760 graphics cards in 2-way SLI mode NVIDIA specifies a minimum of a 700 Watt or greater system power supply that has a maximum combined +12 Volt continuous current rating of 50 Amps or greater and that has at least four 6-pin PCI Express supplementary power connectors. Some of the GeForce GTX 760 cards have a single 8-pin or two 8-pin or one 6-pin and one 8-pin PCI Express supplementary power connectors.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Sufficient Total Combined Continuous Power/Current Available on the +12V Rail(s) rated at 45°C - 50°C ambient temperature...