So I installed an Arctic Accelero Xtreme III on a 290x made sure to follow all instructions etc. even found this http://www.tomshardware.com/reviews/r9-290-accelero-xtr... . So I turned it on and there was a pop and a bit of smoke came from around that part where you plug in the power. All seems to be working fine though, the gpu temp was 30 C. There is also another cable on the heatsink with 07V and 12V on it, I connected that to the power supply. It doesn't say anywhere what they're for but they have that power connector. Is that where I screwed up?
Yes, it seems that is where I screwed up. the cooler has 2 connectors on 1 cable, one you put in the graphics card and the other one is god knows what's for. So the cooler also came with another cable that fits into this second one and has a connector like the one you put the PSU cables into. The black wire is fried and it even broke in half.
That extra connector was probably for the card to supply power to additional fans at 7V or 12V, and shouldn't be used as an input. A picture of that connector would be useful. (You might be talking about the included 4 pin to 3 pin fan and voltage adapter. You can get 7V by using 12V as the positive and 5V as the return, this would just make the fans spin slower.)
If it is still working at all you are probably okay, sounds like you may have shorted out, or just had an air gap from not plugging in the power connector all the way. Cards are pretty well protected from having power cables plugged in upside down and etc as well for just that reason.
If there is a problem with the card, the worst risk is damage to your power supply from a dead short.
On a side note, one of my favorite computer related stories. I had an Athlon Thunderbird at 1.0Ghz that had a dead short. Worked perfectly fine. Pulled several hundred watts through the ATX connector and melted the 12V lines, but worked fine, for a while at least, by soldering new ATX wires to the back of the motherboard. Then the supply failed.