Solution
For a system using a single GeForce GTX 560 graphics card NVIDIA specifies a minimum of a 450 Watt or greater power supply that has a combined +12 Volt continuous current rating of 24 Amps or greater and that has at least two 6-pin PCI Express supplementary power connectors.

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

Overclocking of the CPU and/or GPU(s) will require an additional increase to the combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock.

The OCZ ZT Series 550W (OCZ-ZT550W), with its...
For a system using a single GeForce GTX 560 graphics card NVIDIA specifies a minimum of a 450 Watt or greater power supply that has a combined +12 Volt continuous current rating of 24 Amps or greater and that has at least two 6-pin PCI Express supplementary power connectors.

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

Overclocking of the CPU and/or GPU(s) will require an additional increase to the combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock.

The OCZ ZT Series 550W (OCZ-ZT550W), with its combined +12 Volt continuous current rating of 45 Amps and with two (6+2)-pin PCI Express supplementary power connectors, is more than sufficient to power your system configuration with a single GeForce GTX 560.
 
Solution