Question about Ubiquiti USG: UniFi Security Gateway

Well, the power supply unit is 12 V, they are a dime a dozen (and you usually have some lying around somewhere from other devices). Actually, it's only a question of whether the hollow plug on the USG fits (positive inner conductor, that's practically the case with everything, but there are different diameters - https://de.wikipedia.org/wiki...). You just have to try it out to see if there is a contact.
There are also universal power supplies with many different plugs, but will one fit?

This power supply unit supplies 12V and 1A. Alpha Elettronica plug-in power supply 12 W, 12 V

Take a PoE adapter.