I use the CX500 on my s3's. It's way cheaper to buy many of them. I ran my s3's at 250 until recently went back to stock to accommodate summer heat. Cables would only get mildly warm. You can get a CX500 for $25 currently after $20 rebate.
The CX series is a lower tier psu then the one that OP is using, this isn't a good idea or at least if you home mine and don't want anything to catch fire while you're asleep. I say test the miner and make sure you are using all four pci plugs, weird this happened but I suspect there is an issue on the upgrade kit, could be a faulty issue that was overlooked by bitmain since the kit wasn't popular.
I have ran S3's oc'd on CX500 for over 1.5 years with zero problems.