Yo can be fine with that psu, but 40W for 6970 is absolute bullshit. IT eats a lot of power, i had one once. No metter what cooler you use. Also be carefull with aftermarkets. Although they cools gpu itself very well, vrms will go very high on temps. That is critical for your stability. Also you may be using low intensity with that 6970, give us a screenshot where it shows how much it can mine and temps too.
I did some research re my 6970. There were 2 problems: 1) gpu disabled in Catalyst (not connected to monitor) 2) clock speeds were at 2d speeds (ie much slower than they should have been, a problem others are having with this card, hence forum posts etc).
I did have a dummy dvi plug attached to this card, but it was in the wrong dvi slot. I changed dvi slot, and suddenly the 6970 was enabled in Catalyst (that was easy!).
Once card was enabled in Catalyst, all I had to do was specify clock speeds, and gpuz confirmed that the card was running at the Catalyst clock speeds.
Now the card is consuming more wattage: 250watts, which is still lower than cards with a stock cooler.
With the Arctic Extreme III cooler installed, I've checked the gpuz temps, and all are very low. Screen shots :
https://drive.google.com/file/d/0B5qUFCCYd3cTN3dlajVmb0c3YmM/edit?usp=sharinghttps://drive.google.com/file/d/0B5qUFCCYd3cTdTIyX2wwRGktYlU/edit?usp=sharinghttps://drive.google.com/file/d/0B5qUFCCYd3cTTHk5SmZTbDZiWEk/edit?usp=sharingSo, my journey getting this card working properly is nearly finished, just a little tweaking with overdrive to come.