I think those cables should theoretically support more SATA connections than what they have connectors for, but what are you planning to connect to them? SATA drives?
Only GPU, rx 470 nitro. But as the cable fried so now I am confused if they can handle 3 GPU's on 1 cable....
better not, i would do 1 cable for one gpu , they can sustain around 50w, that's why your cable fried
For the R9 390, you can use that to support 2 to 3 PCIE riser. For the RX 470 or 480, you can support 1.