Hi and welcome to the Forums...
I run my 4090 off an 850W PSU, so the wattage isn't an issue. When you say it's old, do you measn it's been in use for a long time? If so, I personally wouldn't trust my expensive GPU to a PSU on it's last legs.
Also, never use PSU cables from a different PSU, even if from the same company without knowing for sure they're compatible. Some plugs may even fit properly, but be pinned different. That could cause lots of issue's or even failures to the connected hardware or PSU or both. Contact EVGA to see what they suggest.
https://www.evga.com/support/custsupp.asp You may find cables here as well ->
https://cablemod.com/products/
post edited by bdary - 2024/09/12 08:01:28