Ok I understand. I found some really cheap PSUs ( Tecnoware ) 500W PSU for 25....what you guys say about that? If they are ok to use, I would use 1 on each miner.
As I wrote, a really cheap 550W PSU in my case was just a waste of time and electricity and single unit ended needing two of them. If you don't want soldering/modding server power supplies you need to invest in proper single rail PSU that either has constant wattage (24/7) figure in specs or is rated at twice the power you need (750W for single S3)