YoAndy :
280w should be okay till you buy a new one but only if is a good quality PSU, if is not a good quality it could damage your computer.
Ok, I bought a new one it is a MaxPower Silent Power supply 500 Watts Can I use the GTX 750Ti with my 250Psu for a month? Cause Im buying a new Motherboard cause mine has only a 16 pin entry and my PSU has a 24 pins entry, :/ Do you think I can use the GTX for a month? my Psu is 250-280 Watts, Will it damage my GPU ?