I was almost, very surprisingly, going to tell you that was actually a good unit although I had never heard of Xion power supplies. My Who's who of power supplies reference material indicates it being made by Super Flower, who is well respected, however further investigation revealed that while Super Flower does, or did, make a few limited model numbers for Xion, that is not one of them.
That unit is made by Sirtec, and it's not one of Sirtec's better showings. Not that they are well known for quality, but they've been getting better recently, however that unit is too old to be one of Sirtecs more recent, much improved platforms.
Seems according to the data at RealHardTechX, that platform is actually only capable of sustaining about 750w rather than 850w like it's labeling and marketing say. Based off the amperage ratings for each rail, I'd say they had WAY over exaggerated their numbers as well. Looking into this platform I can't find any mention of it or it's platform on the Orion database, Jonny Guru website, our own Who's who in power supplies (Had the wrong info actually) or the RealHardTechX database, other than what I've already mentioned.
This usually means it's pretty bad, else there would be database recognition or a solid review of the platform somewhere. In cases like this I have no choice but to recommend replacement, and as soon as possible, because these kinds of units are generally not well built and while one might last ten years, another may explode into flames taking your entire system and in some cases a lot more than that out with it.
And if you think I'm exaggerating, I'm not. I can show you the money, so to speak.
Anyhow, probably be a VERY good idea to allow for a new power supply no matter what else you do. You really want to try and stick to units made or sold by Seasonic or Super Flower, as those are the two premier PSU manufacturers, and you really can't go wrong with almost any of their own branded units (There are a couple, very few, exceptions) or anything listed on tiers 1 or 2 here (Pay very close attention to EXACT model numbers, because often there are different models within the same series with wildly different quality and specs, built by entirely different manufacturers even though they migh both say they are X or Y series units, just as an example):
http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html
I think there is a VERY good chance that the power supply COULD be the source of your troubles, and not the graphics card at all. Do you know anybody with a solid power supply that might loan it to you long enough to test your system in order to eliminate whether the graphics card still fails or if it works with a good PSU installed?
If so, might be good to try that first. If not, it probably wouldn't be a bad idea to get a new PSU, since you may need it anyway, and then test it with your current GPU card to see if the problem goes away or remains. Might not even have to get a new card, unless you want to anyhow.