I have a similar case and similar concern. I also noticed the way in which the supermicro PSU is mounted in the case. Both the case and the power supply appear to be using proprietary mounting points, which to me makes no sense, given the ease of mfg where the manufacturer could adapt to the mainstream format of "normal" power supplies. This is not a server specific power supply or design with respect to the power supply.
Have you come up with a solution so far?
I just came across this forum...(1) what happens when supermicro no longer furnishes the OEM power supply.. the only solution I've pondered...so far is to come up with some type of adapter where you would essentially have to rig something to support a conventional power supply.
I too noted the unusual mount points of the OEM power supply and I was going to swap out to a "normal" power supply but put that on hold as I looked around to see what anyone else has done.