Apple Watch charger not charging
You have to do some basic trouble shooting.  You have two components to check:


The 12v power port in your car
The charger


Plug your charger into the power port of a different car with a power port you know to be good.  If your charger works, then the problem is related to your car.  If it dosen't work, then your charger is at fault.

Alternatively, you can plug a known working charger into your car.  If it works there as well, it's your charger.  If it doesn't, it's your car.