Faulty SuperFlower but I can't prove it - options?

[Matmulder]

Bit of a long shot, but thought I'd ask...

My SuperFlower Leadex 550W was shutting my system down under load (gaming) when its 21deg or warmer in my spare room. I've proven this by swapping to some cheap Corsair unit from a mate and my system has been 100% stable.

The SF has 3.5 years warranty remaining, and despite some disagreement between SF and OcUK as to where to send for warranty, OC took it and stress tested it - obviously it passed all tests as I suspected it would.
So I had it back, plugged it in (in some vain attempt at hopefulness) but sure enough, 5 mins into games the PC shuts down. Corsair back in - solid.

I'm not blaming OC here - if it passes their tests there is nothing they can do; but does anyone have any suggestions before I throw £100 worth of PSU in the bin? If I'd have known I'd have been replacing a PSU every year I would have bought a disposable cheap one

 

[Matmulder]

Coolermaster aluminum case - It's at the top of the case, fan down. No filters, and it happens both on eco and normal modes. I've even tried running it outside of the case, no difference - still shuts down when gaming.

Super Flower have said I can return it direct to them for testing, but that's in Germany; I've already paid once to send it back to OCUK so reluctant to keep throwing cash at it as they need to prove the fault too. They've also told me it'll operate at upto 40deg ambient before shutting down, but it's not getting anywhere near that, I've felt it and it's barely even warm to the touch - but definitely ambient temp related, as it runs fine during the cooler weather when the house is cooler.

I'm not going to sell it I'm not that much of a jerk. I mean, it'll run as a non-gaming PSU just fine, but I'd rather just keep it as an emergency backup.

 

[Matmulder]

System had been running for 12-14 months without an issue.

i5 2500k (no longer overclocked, as I thought that was what was causing the issue originally)
Asrock z68 extreme4 gen 3
8GB RAM
GTX 980
2x 128GB SSD, 1x 2TB HDD

Case is a Coolermaster Wave Master TAC-T01-E1C (which I bought years ago!)

The PSU I'm running now is a Corsair CX600, and that's working fine...it's much cheaper PSU.