For a system using a single MSI Gaming N770 TF 2GD5/OC GeForce GTX 770 graphics card a minimum of a 550 Watt or greater system power supply that has a maximum combined +12 Volt continuous current rating of 35 Amps or greater and that has at least two 8-pin PCI Express supplementary power connectors is recommended.
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.