While it may be surprising to hear this, PCIe Gen5 graphics cards will require either a 16 pin or an 8-Pin to 16-Pin” adapter to operate properly. Fortunately, these cables are very similar. The two are physically identical and are the same size. Next-gen GPUs will be required to use either a 16-pin or an eight-pin power cable. It is likely that there will be no need for adapters for this reason.
There is no official information about the PCIe Gen5 power connector, but many companies have suggested that it may be required. A triple 3×8-pin to 16-pin adapter may be necessary for those upgrading to PCIe Gen5, though NVIDIA has not confirmed whether its power cable supports this new standard.
While the official PCI-SIG PCIe Gen5 power specification has yet to be released, the GIGABYTE 16-pin (12+4) connector is very similar to the standard 12-pin connector. A double-sided adapter may be necessary for some applications.
Unlike the eight-pin connector, the sixteen-pin power connector is more efficient. It can handle modern graphics cards with ease.
The 16-pin cable is also more compact than the eight-pin connector and can deliver more than 600 watts of power. A sixteen-pin power cable will reduce the number of cables in a system and simplify system design. It is also more convenient to use when installing new hardware.
Source: Videocardz
