Beware how you plug in power supplies into your PC motherboard especially PCIe vs CPU 8
Compatibility issues for ATX power supplies and motherboards
Modular vs Non Modular PSU
How to Choose Power Supply for PC: What to Know
At least that's true unless you try really hard to force it into the connector.
Reliability and Efficiency In theory, using detachable power connectors vs hard wired connectors for regular power supplies will increase electrical resistance and therefore lower the efficiency of modular power supplies.
Pinout Pin number Wire number Wire color Description 1 5 orange +3.
But if you don't have any other information then just assume that if your video card has an 8 pin connector then you must plug in an 8 pin cable.
Others will work with a 6 pin cable at normal speeds but will not allow overclocking.