I'd bet a PSU that it's your PSU.
AMD FX-8350 can easily exceed 220-230W under heavy loads.
780Ti with mild OC is like 260-290W.
You are definitely exceeding what that unit is capable of... Cheaper units may advertise 680W, but the actual max output on +12V rail will be somewhat to a lot less than that.
Personally, I would avoid Corsair. I was a very loyal customer of theirs starting with my A64 FX-51 rig back in 2003, and they truly did make THE best memory for those chips, no question.
Over time, however, they've grown, they began to stick their fingers into as many pies as they could, from memory to SSD's to enclosures to PSU's to gimmicky "sooper l33t g4m3R g34R", all the while coasting on the reputation they built for their name years ago instead of actively ccontinuing to make that rep even stronger. Now, they're selling vastly ooverpriced memory that almost always underperforms against GSkill, mediocre SSD's, PSU's that are either way below anythingelse in their cclass or decent units overpriced like a bad joke, and so on.
Thetthing is, all those products (PSU/RAM/SSD), they don't actually make/manufacture... They simply buy and rebrand, adding the required "Corsair Tax". You truly are paying for a name, not quality.
I would STRONGLY recommend that you get an EVGA 850G2, it's an excellent unit and the price is definitely right. You could up it to the 1000G2, but it is notrreallynnecessary unless you intend to SLI...