Thanks! So I will power it directly from the PSU, as I have one 6+2 connector unused.

Should I also plug in the molex into the motherboard?

Hi,

I bought a usb riser with a 6pin connector. It came bundled with a 6-pin to SATA adapter. I want to use it to connect an r9 390 to my motherboard (its two 16x slots are occupied by an rx480 and an rx580). I tried using the riser with the included adapter, but the system would power-up for a second, a led would flash on the riser (I was terrified when I saw it as I thought it was some kind of a short, but then I noticed the led...) and then some sort of protection would kick in and the system would shut down completely.

1. The motherboard (AsRock) has a molex socket. Should I plug in a connector from the PSU?
2. I read that it may not be a good idea to use the 6-pin to SATA adapter to power the riser. What should I use instead? Is it possible to connect a 6pin directly from the PSU?
3. Will an rx480/580 draw less power from the PCIE slot than the 390? Which would be best to use with the riser?

Thanks a lot!