G-Sync: NVIDIA monitor synchronization technology, compatible with Freesync.
FreeSync: AMD monitor synchronization technology
Adaptive-Sync: compatible with G-Sync, FreeSync
The principles of G-sync and Freesync technologies are the same. The difference is that G-Sync is a technical standard of NVIDIA, and Freesync is an open-source technical standard. Therefore, as long as the display manufacturer can use Freesync technology free of charge, but to use G-sync technology, you must pay NVIDIA to get the technology license. This is why G-sync is more expensive than Freesync.
But don’t worry, if you pay the money, Nvidia will do things for you, that is, check whether the G-sync monitor is qualified and whether the components used are compliant, so the G-sync monitor has quality assurance. On the contrary, the quality of Freesync displays is uneven, because Freesync technology is open source and no one manages it uniformly.