For a system using a single GeForce GTX 660 (non-Ti) graphics card NVIDIA specifies a minimum of a 450 Watt or greater system power supply that has a maximum combined +12 Volt continuous current rating of 24 Amps or greater and that has at least one 6-pin PCI Express supplementary power connector.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Combined Continuous Power/Current Available on the +12V Rail(s) rated at 45°C - 50°C ambient temperature, is the critical factor.
Overclocking of the CPU and/or GPU(s) will require an additional increase to the maximum combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock. The additional amount required will depend on the magnitude of the overclock being attempted.
The GIGABYTE PoweRock 500W (GE-N500A-C2), with its maximum combined +12 Volt continuous current rating of 36 Amps and with two (6+2)-pin PCI Express supplementary power connectors, is more than sufficient to power your system configuration with a single ASUS GeForce GTX 660 Direct Cu II TOP 2 GB graphics card.
If you're curious the OCP (i.e. Over Current Protection) set point for each of the +12V rails on the GIGABYTE PoweRock 500W (GE-N500A-C2) is set at 27 Amps.
The ASUS GeForce GTX 660 Direct Cu II TOP 2 GB will draw less than 11 Amps from the +12V rail even when running Furmark or performing heavy GPGPU processing so you shouldn't be inadvertently tripping the OCP circuit.