12vhpwr adapter bad idea?

So I am working on upgrading my pc and looking at power supplies. I see that some of them support PCIE 5 power and some do not. So my question is, if I get a PSU that is on the old standard and I later buy a GPU that only has PCIE 5 power, is using an adapter to fit the old power supply to the new GPU a bad idea? Or is this generally something that would be OK assuming quality components?