My colleagues have been running Rx 580 Sapphire with 2 PSU-s x 750 watt each Modular from the Cooler Master brand. They all have connected the risers with Sata cables and they have been running from about 2 months and a half without problems.
.........
That's similar to what I had, two PSUs with a Y adaptor to the motherboard. Then RX580s on risers with Sata adaptors.
I too thought 'everything was fine' and ran 4 months almost continuously with minimal problems. I thought I wouldn't have issues but then here I am with the costs of replacing the PSU and a riser and the fact the rig did - in essence - fume while unattended.
I bet if your colleagues touch the left hand side of the plastic sata adaptor it will be very hot, not a good sign.
Tbh, I use SATA (one rail one risers) for my R9 Rig, running smoothly for more than one years. But yeah, personally I wouldn't recommend it, that isn't a standard setting for safer. I'm doing it with a lot of trial & error, lucky am I, the whole of my R9 seems like isn't type of cards that load full power from PCIe bus.
So, you were in the right decision, buddy.
This is also can be your another option if you can get cheaper server PSUs in your area.
I'm buying upgraded server power supplies. They are cheaper and can withstand heavy load for a long time. Several times I had problems with the power cable. Cheap cables from China dry up and break. I changed them to high-quality and no more problems I had. Now I am in all my rigs use such power supplies.
