For the EVGA GeForce GTX 950 FTW ACX 2.0 (02G-P4-2958-KR) the system power supply must have a maximum combined +12 Volt continuous current rating of 25 Amps or greater and also have at least one 150-Watt 8-pin PCI-E Supplementary Power Connector.
Total Power Supply Wattage is NOT the crucial factor in determining power supply adequacy!!! Sufficient Total Combined Continuous Power/Current Available on the +12V Rail(s) is the most critical factor followed by a sufficient quantity and type(s) of PCI Express supplementary power connectors.