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.
An exception is the MSI GeForce GTX 660 HAWK 2 GB. It requires two 6-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, is the most critical factor.
The Cooler Master GX 550W (RS-550-ACAA-D3) power supply unit, with its maximum combined +12 Volt continuous current rating of 44 Amps and with two (6+2)-pin PCI Express supplementary power connectors, is way more than sufficient to power your system configuration with a single GeForce GTX 660 (non-Ti) graphics card.
Hopefully you don't have the unreliable RS-550-ACAA-E3 model that was made by Seventeam.
The RS-550-ACAA-D3 model made by Enhance Electronics was suppose to fix some of the problems with the RS-550-ACAA-E3. The newer model is also more electrically efficient.