Ummm, actually, *mine* *did* require an external power source....
Welcome to Visiontek: Unbelievably Real Graphics
System requirements: 350W PSU....
I burned up my 250W testing it (just had to try) and then bought an XPower 500 that bit the dust so I then got a MadDog Multimedia 500W Modular PSU that I still have in the case with the card. Works perfectly (albeit a bit slowly) on Vista.