https://wccftech.com/apple-watch-series-7-requires-new-5w-or-higher-usb-c-pd-adapter-for-fast-charging/

If you ordered the new Apple Watch Series 7, there are some things that you should take note of related to the fast charging speeds. Since the Series 7 comes with a new charging architecture for faster charging speeds, it required a new USB-C charging adapter Take note that the new USB-C cable is included in the Apple Watch Series 7 box and Apple also sells it separately. Scroll down to read more details on the subject.

As mentioned earlier, Apple's new charging architecture will allow the Apple Watch Series 7 to charge 33 percent faster compared to Series 6. For reference, it can be charged from 0 to 80 percent in just 45 minutes. However, the Apple Watch requires a new USB-C power adapter to take advantage of the fast charging speeds.