Best Wattage USB-C Power Adapter

Any USB-C power supply will work. It can be less than 20watt, and the Series 7 will just charge slower. It can be more, all the way up to and including the 140watt 16" M1 Max MacBook Pro USB-C charger.

The Apple Watch will take what it needs and no more.

20watt USB-C will enable Fast charging.

The 20 Watt from Apple is supposed to be the best one. There are a few reviews of it on YouTube!

what about 30watt adapter USB-C came with my McBook air ?