Thats not a problem as long as you plug in both PCIE cables from the same PSU to the back of the Apollo, and the PSU has at least 200-300 watts headroom for the Apollo.
Issue come in when you try to plug in two separate power supplies in the back of the Apollo (ie some people think if they have 100 watt headroom in one PSU, and 200 watts in another, they'll just plug in one PCIE cable from each PSU to the back of the Apollo...THIS IS THE FIRE HAZARD. Even a small imbalance in voltage will cause major current to flow between the PSUs and melt the cables/start a fire.
Emphasis mine.
Ja. One should NEVER try to run ANY sort of PSU's in parallel. Because they are independent devices they will literally fight each other. If you want to run PSU's in parallel they MUST be designed for it (master-slave modes) and wired accordingly.
GPU miner here, been running dual PSUs for last decade. My typical rig consists of one motherboard, 6 or 8 cards, two PSUs 650-850W each, for total of 1100-1200W per rig. They are running for years on end, without any reboots.
I presume you just speaking from what you heard, not real experience?
I agree, that running two PSUs on one electrical device (like one Apollo or one GPU) is a no no. But don't extrapolate that to "One should NEVER try to run ANY sort of PSU's in parallel" (your quote), because that's BS.