Yeah, that's why I was confused. The GPU arrived with a DVI/VGA adapter and a power cable (6-pin to 8-pin) adapter included, but no extra power cables .Nor did the web shop say anything about needing an extra cable. Since my old card required only a single power cable, I assumed this one did too.
One problem is that my power supply doesn't have any free slots, so I'll have to take power from one of the cables already in use. Meaning I'll have to buy one of
these puppies, connect it to the PSU and have that same cable power both 1/2 of the GPU and something else I'll try to buy quality so there isn't too much power going through the cable, to reduce the chance of overheating. I'm not sure drawing all the GPU's power through a single cable is a good idea.
I really hope this solves it, but even if it does, I guess it's time to think about buying a new power supply too... I'll put it on my "future to-buy" list.