That PSU is junk and the cards having no spacing is causing your heat issues. Time for new case and PSU
Take the powersupply back and ask for a refund, it can't power your graphics cards so it's unfit for its purpose. Not sure about laws in the states but if anything here doesn't do as described or is drastically different to what's on the box, you can take it back and ask for a refund, and the retailer HAS to comply. Otherwise you ring up the ACCC and complain, retailer will get a fine or some other discouragement for not honouring the laws. I guess you'd be going to the BBB.