The S12II isn't among SeaSonic's flagship PSU's (it's not a bad PSU by any measure). It's likely an internal component in the PSU died prematurely (it happens). It is for that reason that you purchased a higher quality PSU, contact SeaSonic about RMA, they should have you covered.
I doubt your PC killed the PSU, if anything I'd suspect the MOV was working too hard (result of wonky mains voltages) and finally gave up the ghost (just a guess - could be a number of things)