Technically, EVGA recommends plugging a separate cable into each port for their GPUs. I can not tell you how much digging and searching it took to find that answer.
Also, Linus Tech Tips On YT (I think that’s the channel) did a video where he was using the pig-tailed cable on his 1080ti and it was running fine. He then switched it to using 2 separate power cables, not expecting to see any change, and was surprised to see a small bump in hashrate. In my personal experience, I’ve seen my FTWs show slightly better numbers than the SC2s, even when they were both on pig-tailed cables, so I decided to go ahead and do separate cables for them based on the Linus Tech Tips video. If I had one more port on the PSU, instead of 2 CPU ports, I would run the 1080 on 2 separate cables also.
I power the risers using the 6pin to molex cables, 2 risers powered on each chain. I read not to go over 2 per chain so they don’t draw more than the cable can handle. I wish EVGA sold 6pin to 6pin cables individually, but I feel better using EVGA’s supplies 6pin to molex than trying a 3rd-party’s cables to power them from 6pin.