What I am saying, u draw very little power from the USB ports, so it will run just fine.
If it runs now, it will run with the USB card.
USB 2.0 can deliver 500 ma at 4.4V - 5.25V
USB 3.0 can deliver 900 ma at 4.4V - 5.25V
For your GT 545 (DDR3) = 350W is recommended by manufacture. So, decent 300W PSU will power it just fine.
Will 240 watts do? I can get a 330 watt PSU but I'd like to save my money.