I would suggest installing a GFI receptacle to feed your PS if you cut the grounds from the 115v supply. A GFI compares current flow from hot and neutral, so no ground is needed. If any of the cases become energized for any reason, your regular circuit breaker will not trip and when you touch the case you will do the "60 cycle shuffle". If a GFI is installed it trips with leakage as little as 5 milliamps or so,mimizing risk to you and equipment. I was unaware that the DC circuit of PC power supply had any connection to ground, and if no ground is needed to operate then why is it connected in the first place ?
Steven