620 Watts Enough

it will be more than enough

A 620w Antec? You could probably run 3 560ti's on it.

For a system using a single GeForce GTX 560 Ti 448 Cores Limited Edition graphics card NVIDIA specifies a minimum of a 550 Watt or greater power supply that has a combined +12 Volt continuous current rating of 38 Amps or greater and that has at least two 6-pin PCI Express supplementary power connectors.

Total Power Supply Wattage is NOT a crucial factor in power supply selection!!! Total Continuous Amperage Available on the +12V Rail(s) is the most important.

Your Antec High Current Gamer Series 620W (HCG-620), with its +12 Volt continuous current rating of 48 Amps and with its two (6+2)-pin PCI Express supplementary power connectors, is more than sufficient to handle your system configuration and has plenty of reserve capacity to handle any overclocking of the CPU and GPU you may want to perform.