I think, they're different because they're different things.
The xml tries to mimic the Google style guides using IntelliJs built in code formatter and is written by a third party. The plugin comes directly from Google and seems to be a wrapper around the official formatter by Google as there are plugins for other platforms as well.
To be as close as possible to the code style, I'd suggest the plugin over the xml.
I'm used to using Prettier but it seems they have no Java support currently.
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