Your problem is, most likely, your PSU. It is capable of handling the load at idle but not when you stress it at gaming. Your present PSU may be OK for some low end systems, but you should swap it out for a better quality, more powerful PSU.
I've already tried running the GPU at 100% fan speed, it still reaches above 80c.
As for PSU, the wattage isn't mentioned anywhere on it, so no way of knowing.
Of course it's mentioned, but since your unable to find it, have you tried googling the brand and model number?? It's really not that difficult, we can't do it for you unless you post the brand and model number.