I just bought a SFP Transceiver (on Amazon) to connect an optical fiber between 2 CISCO switches (2960x). The SFP is detected as "Type : unknow". Do you know if I inevitably must buy a CISCO SFP Transceiver ?
There is a "service unsupported-transceiver" configuration command that you can apply (at least on some models and IOS versions) which will allow you to continue to use transceivers manufactured by other vendors.
This will, however, cause a syslog message to be emitted, and if you open a TAC case, however, the service rep may ask you to use a Cisco transceiver instead.
Now you don't have to buy a Cisco transceiver but you can't plug any transceiver either.
The transceiver firmware must include a Cisco specific tag to be recognized by the switch / router.
So when ordering you must ensure the transceiver is noted Cisco compatible and check if there's more precise compatibility information.
Check your device transceiver module compatibility matrix.
Output is extensive, check here
If you ever run into a case with TAC they might ask you to swap for a Cisco SFP.