From looking at EVGA's Web site for a GTX 750Ti, it shows 4 different models.
Two of them state:
Requirements:
Minimum of a 300 Watt power supply.
Total Power Draw : 60 Watts
Then two others that seem a bit more power hungry-
Requirements
Minimum of a 300 Watt power supply.
Total Power Draw : 85 Watts
I'd say you were pushing the PSU to it's extremes with the 275w when EVGA is recommending 300 watts.
What are you using now for a graphics card?