USB-C power adapter isn't charging my Mac notebook

Try an SMC Reset if you have an Intel Mac.

Disconnect all external devices from the laptop.

Make sure to connect the charger directly to the laptop since a multi-port adapter, dock, or hub may not allow the charger's full power to reach the laptop. Try each USB-C port especially on the other side of the laptop if you have four ports. Also try rotating the USB-C connector 180 degrees upside down (I know it sounds crazy, but it can make a difference sometimes).

Try unplugging the charger from the electrical outlet for a minute to reset the charger's internal circuitry.

Here is an Apple article for troubleshooting USB-C charging issues:

https://support.apple.com/en-us/HT204652

If you find any ports to not work correctly, then you will need to have the laptop repaired.