Is My 20W Adapter Original?

Did you buy the adapter from an authorized Apple dealer? You can find a list of authorized dealers in your area using this link:

Find Locations

I think you will be disappointed at the Apple Store because Apple does not track serial numbers on accessories like this. The store can check the device to see if it is charging an iPhone, but you can do that yourself without having to make a trip.

If you are still unsure about things, buy a new adapter when you visit the Apple Store.

Appears to be genuine, but the only way that you will know for sure is if you bought from an authorized Apple dealer and you have a receipt indicating the model number for the device.