IT is an AC output for lighting
At first glance it might appear to be a 3 phase but it is not because there are only 2 coils. I suppose it's a 2 phase output!
I will attempt to post a photo of the section from my manual ( for an ordinary 6hp engine) that shows how to use the socket for lighting.
If you want to use the output for battery charging it may be possible to get the rectifier kit which plugs into the socket but you don't get a lot of useful power. I now use a small solar panel for battery charging. That works all the time and every day of the week while the sun is shining , not just when the engine is running.
Otherwise it would be possible to disconnect the socket and fit a 4 wire rectifier directly to the output from the stator coils
Or if you know what you are doing construct a 3 phase rectifier from 6 suitably rated diodes
