**** Below Message which I copy from some serious miner, their practice like Nestorius, for ground issue, seems riser should connect with the PSU which connected to the motherboard board only **
They stated ground issue which is not the same as you said....
But their operation is same as Mr. Nestorius....
I am not professional in electricity..... I do want to know the real answer as safety should be on first priority *************
I recently upgraded to a dual power supply setup which had me researching on how to connect them safely.
I came across posts suggesting powering the riser and PCI-E power connector on the card with the same PSU. Others say the psu that powers the motherboard must also power alll the risers. The slave psu should only power the PCI-E power connector on the cards.
Ultimately, I did follow the latter suggestion as it seems logical the same power supply that powers the motherboard should also power the risers connected to the PCI-E slots on the motherboard. The second slave power supply only powers the 6 & 8 pin auxiliary power connector on the video cards. According to another post I came across that connecting the PSU's that way ensures they share the same ground, which is important.
I also noticed BBT in his latest live stream set up a 9 card dual PSU rig and also explained that when setting it up, you need to power the risers with the same PSU that powers the motherboard and only use the second PSU to power the GPU's.