Thunderbolt Display Glitches [Round 2]

Hey guys,

So I have a late 2012 iMac w/ a 27" Thunderbolt display that I picked up last May, and I've been having continual problems with the pair for the last month, and I'm tyring to figure out what the source of the problem is. So the initial problem I had apparently was a faulty power supply– I was out of town and came back to it dead. It happens, took it in, and got it covered under warranty– all is well. Things go ok for about a week, but then the working in photoshop, certain files only would start to glitch out when dragged to the thunderbolt display. Unplugged from the imac and plugged back in, and it seemed resolved. It would happen a couple more time, but would get fixed the same way. Now, the whole screen is getting scrambled and the whole screen is glitching and flickering without anything even on it. It's become entirely unuseable. Here's a video of the screen in action (sorry for the terrible portrait view video, the frustration has clearly clouded my judgement): https://db.tt/v7E6OjQe

So my question is:

What do you think the likely source of the problem is? Faulty video card? I ran a hardware test and it all came up OK, so I'm not sure it's that, but it does seem likely given the symptoms (from my novice level knowledge of them). And naturally any suggestions to resolve it?

Any help would be greatly appreciated it.

Thanks,

Jon