The key is the 12V-line on your PSU. It should have the necessary GPU power plus 50% safety margin. The GPU power is defined by its TDP. If you don't tweak with it that's pretty accurate - at least for NVidia cards.
The TDP for a GTX960 is 120W, GTX970 -> 145W, GTX980 -> 165W.
A problem are the power peaks, which can draw up to 50% of the original TDP for a short time.
That is why you need enough power headroom.
The TDP for a GTX960 is 120W, GTX970 -> 145W, GTX980 -> 165W.
A problem are the power peaks, which can draw up to 50% of the original TDP for a short time.
That is why you need enough power headroom.