Okay thanks for the infoHaving dual 12V rails does not necessarily mean each PCIe connector is on a different rail. For your PSU both PCIe connectors are on the same rail, so it doesn't matter which you use.
https://www.tomshardware.com/reviews/be-quiet-system-power-u9-500w-psu,6035.html
Okayy thenn, thankss for the infooPSU isnt the best, but its fine.
It doesn't matter what connector you use.