With 500W Power Supply
Tells us sfa really.
To err on the side of caution, I suspect it could be a yum-cha spec 500W (low 12V amp, not true 500W etc)
You should be able to run the card, but stay away from overclocking etc High loads for extended periods (ie Folding@home etc) is also not advisable.
For longevity's sake though, I'd consider a 'brand' name PSU sometime in the future if budget is a pressing concern now.