I have still some questions here. I used one of the PCIe cables that has two x 62 pin at the GPU end. Just like mentioned here, second picture: https://www.gpuminingresources.com/p/psu-cables.html

according to this, 288W per cable is fine. according to the TDP of the 3080 it is 320W. When card reaches 320W it pulls like 50W off the riser. 270 left, which should be inside the 288W with a single cable?

nevertheless: I picked  up a second PSU as currently I cant get my hands on a single 2400w psu atm. This one has 3 of those cables so I powered 3080 with 2 of them and the 3070 with one. now Im paranoid that I need 2 more cables, 3 dedicated for 3080 and 2 for the  3070.

I thought about that the CPU EPS12V ports aint used and that with such an adapter: https://www.caseking.de/kolink-adapter-6-pin-pcie-auf-eps12v-8-pin-cpu-anschluss-schwarz-10cm-zuad-765.html

I could supply 2 extra cables for cpu. I know it says adapters are shit in general but this one should be one of the good guys?!