My PSU is an 850w EVGA supernova, it comes with 2x PCI power cables both are 8pin from the PSU and terminates as 8 pin (6+2) and 6 pin on each cable, the Graphics card I am looking at getting (RX 7800XT) needs 2x8pin, can I just connect 2 x PCI power cables to the PSU and use the 8pin (6+2) on each cable (leaving the 6 pin on both unused). Alternatively can I just get a new PSU cable that is 8pin from the PSU with 2 x 8pin on the other end to connect to the Graphics card?
It’s all on the 12v rail so it shouldn’t matter, should it?
I don’t know about the 8->[6+2]+[6] cable situation. I haven’t seen those. 8->[6+2] is fairly common though, as is 8->[6+2]*2 (some call it a pigtail).
The main advantage of the pigtail cables is that they use a single 8-pin on the PSU, and it’s only one cable.
The main disadvantage is that this single cable has to provide all the power required by the GPU, which means it will be carrying all the current and will get hotter. This reduces the longevity of the cable and could become a fire hazard depending on the quality of the components.
Running 2 cables in parallel means each cable carries one half of the current, which should be safer.
In reality whether any of this will become a problem depends on all the parts involved, but if you have the option, 2 cables is always going to be safer.