What alternatives are there for charging my Apple Watch Series 9?

There is no other way to charge an Watch than with the Apple or a compatible 3rd party charging puck.

M1 Mac mini, macOS 14.5;  Watch, series 7 GPS/cellular, watchOS 10.5; iPhone 12 Pro, iOS 17.5; TV 4th Gen, tvOS 17.5; HomePods, audioOS 17.5 and Airport Express w/ Airplay 2

3rd party watch pucks aren't going to burn anything! I've successfully used them for years.

Either they work or they don't. watchOS has gotten better lately at recognizing and charging with 3rd party charging pucks.

You don’t wanna burn your Apple Watch from using 3rd-party chargers

just get the official cable