I am currently running my card on the Corsair HX850i. The two PCI-E GPU power cables supplied are only sufficient for one card. Each cable has two connectors at the end of the graphics card that work for both the 6-pin and 8-pin connections of the graphics card. So you "bridge" from one cable to two sockets of the graphics card so that the sensors for the power supply are satisfied. (Normally, you shouldn't need much more than the 300W that you can draw from the 2x 8-pin connections according to the specification, unless you are an extreme overclocker with LN2 cooling).
Depending on what else you connect to the PSU, you actually have enough ports free on the power supply to connect two more cables like this. But then you would have to buy a cable kit for the PSU. For example something like
BitFenix Alchemy 2.0 PSU Cable Kit, CSR-Series (I don't know if you can get the cables separately in modding shops, here at Digitec I didn't see anything).
Also, depending on the system and overclocking, you should probably consider a 1000W power supply if you want to install 2x 2080Ti in the system.
Hope this helps...
