NVIDIA 40 Series & onwards (NGREEDIA will implement this connectors for future cards) uses a new connector than the older Series which uses the standard 6+2/8-Pin EPS/PCI-E Connectors.
If you are using an older PSU, you won't have any PCIE5.0/12VHPWR cable(pic 2). Only newer PSU already have them implemented. But you can purchase the Adapter(pic 1) in which it uses 3x 8-Pin EPS/PCI-E to 12-Pin (top 4Pin I don't count as it's mostly signal pins) 12VHPWR
If let's say your PSU is a low wattage & only have 2x 8-Pin PCI-E Cable, I will say, good luck in trying to power the new gen gpu. Or if you lost 1 of the cable, good luck as well.