I recently upgraded my GPU to an ASUS Prime 5070ti, but I ran into a problem with my previous Power Supply not having enough PCIe cables, resulting in a red light and no display. I then purchased a Corsair RM850X PSU, which has a 12 pin input that fits the GPU, and I've connected everything as follows: the ATX cable to the ATX and motherboard slot, the ATX12V to its respective spot, the 12V-2x6 pin to the GPU and PSU, and SATA for my SSD and HDDs. I now have some unused PCIe cables left over, and I lost the adapter for the GPU. Given my setup, do I need to use the PCIe cables, or can I start the system up without them?
3 Answers
Quick bonus question: Will moving from a 750W to an 850W PSU cause any issues with my setup, like needing to tweak BIOS settings?
You're right, since your GPU uses the new connector, the PCI-E cables aren't necessary. Just keep them stored away in case you need them later or if you decide to sell the PSU down the line.
Good point! Wish I had held onto the PCIe cables from my old 750GT Supernova. I’ll make sure not to let that happen again!
No, you don’t need the PCIe cables for your setup. The 12V-2x6 cable you used is sufficient for the GPU. I have a similar PSU, and it works fine without those extra cables.
Thanks a lot! I’m crossing my fingers that everything runs smoothly and there are no issues when I power it on.

No, you shouldn't face any problems like that. Just make sure not to mix up cables from your old PSU with the new one, and you’ll be set!