Replacement Graphics Card

I have a Dell Studio XPS 8100.with an NVidea GeForce GTS 240 Graphics Card, the fan of which has broken. The card works fine till it overheats and shuts down the computer. I was looking for a replacement card and found a GeForce GT 630 card which seems to fit the bill. It has 2GB of video memory so would appear to also be an upgrade to the 240. However when I checked the minimum system specs, it needs a 450 watt power supply. My Dell came with a 350 watt PSU. Strangely however, when I checked on NVidea's website about the minimum power requirements of the original GTS 240 card that came with my Dell, that also needs a 450 watt supply. What gives? Can I  then safely use the new GT 630 with my current PSU and not worry about it, on the grounds that a 450 watt graphics card has happily worked for 3 years on the 350 watt PSU? or has the GTS 240 somehow been downgraded to draw less power by Dell before being fitted.

Another option I've considered is just fitting a separate PCI fan to cool the old card which as I said still work fine a long as it's cooled. Or even bodging up a separate CPU fan under the Graphics card, but how would I power this as both fan connectors are taken up. Are there fan power connection splitters available or fan power adaptors available to run straight off the power supply.