Xfx 4870 wont boot with two power cables plugged in

Hi,
I just build myself a new system, and was mortified when I saw that the psu I bought only had one pcie power cable and my shiny new xfx 4870 1 gb needed two! I thought I'd give it a try anyway, and the system did boot. It was at this point I found the molex to pcie adaptors in my case, so I took an adaptor, plugged on two different molex cables. Now the graphics card wouldn't work - the fan seemed to be running but at much lower speed than before, and nothing on the screen. When I took out the extra power the card ran again. I tried all sorts of different combinations with the adaptors, but the card would only run if only one power source was plugged in. What should I think of all this? I read a review of a4870 card somewhere where they had the same problem but it performed well nonetheless.

Really? I figured 600W would be sufficient... so what should I aim for?

On the side of your Power Supply Unit, there should be an electric rating label.

There should be a +12V rating on the label.

For example, +12V could be represented as 26 Amperes.

I strongly suggest that you find out the ampere reading and tell me the answer.

Perhaps your Power Supply Unit is not feeding enough power to your 4870.