For a system
using a single GeForce GTX 550 Ti
graphics card NVIDIA specifies a minimum of a 400 Watt or greater power supply that has a 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) @ 50°C ambient temperature, 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 additional amount required will depend on the magnitude of the overclock you are trying to achieve.
The Antec High Current Gamer 400W (HCG-400)
, with its combined +12 Volt continuous current rating of 30 Amps
and with one 6-pin PCI Express supplementary power connector
, is sufficient
to power your system configuration with a single GeForce GTX 550 Ti