Get rid of that PSU now! There are marginal PSUs, crap PSUs, POS PSUs, firecrackers waiting to happen, Huntkey PSUs, then Deer PSUs. Huntkey PSUs are actually dangerous, not just for your system but also for you, they don't fail nicely, especially not their cheaper ones. Here is a list of reviews of huntkey PSUs similar to yours
http://www.hardwaresecrets.com/article/668
http://www.hardwaresecrets.com/article/527
http://www.hardwaresecrets.com/article/1004
http://www.hardwaresecrets.com/article/754
Note the page titled "The Explosion" in the first link.... Almost all of the huntkey PSUs reviewed have failed catastrophically at load levels that they claim to be able to deal with.
Your PSU is also only a 400W rated PSU with passive PFC, its going to be rated for 25C like the rest of them, so you are going to lose about 1.2W/C. If you are going to spend money on a new GPU, drop the $30-40 to move up to a real power supply that can actually power it.