For me , I am running 9GPUs rig and I have connected 5 Riser to Primary PSU (mobo one) and 3 riser + 5 GPU on 2nd PSU . Yes early I have connected 3 Riser on 1 Sata Cable and my cable got burned but after 1 1/2 months later, now I switch 2 Riser per Sata cable and its running fine from last 1 week.