For a system using two reference design GeForce GTX 560 Ti graphics cards in 2-way SLI mode NVIDIA specifies a minimum of a 700 Watt or greater power supply that has a combined +12 Volt continuous current rating of 52 Amps or greater and that has at least four 6-pin PCI Express supplementary power connectors.
For two factory overclocked GeForce GTX 560 Ti my minimum recommendation would be the Corsair Enthusiast Series TX750 V2 (CMPSU-750TXV2), with its combined +12 Volt continuous current rating of 62 Amps and with four (6+2)-pin PCI Express supplementary power connectors, is sufficient to power your system configuration with two GeForce GTX 560 Ti in 2-way SLI mode.
Guru3D doesn't measure their maximum power draw when using FurMark or some equivalent GPU stress testing utility anymore. If you never run FurMark then the +12 Volt continuous current rating of 52 Amps will be sufficient. If you do run FurMark, for whatever reason, then you will need a +12 Volt continuous current rating of 62 Amps or greater if you don't want the PSU to shut itself down because the OCP gets tripped.