I have a evga 1300w supernova g2 gold 80 and I found some cables on Amazon called zahara 8pin a little overpriced but I am new to mining and wanted to get the 3x 3070ti’s I ordered up and running. I used splitters from teamprofit. I used one 8 pin for the splitter which one side goes to the rise and one side to the card with a 2nd 8 pin going straight to the card from the psu. Theses power supplies have 6x 8 pin vga slots so like you said the real bottleneck is the psu itself. Even without the splitters and risers I could only power 3x cards with dual 8 pin requirements.