120v to 12v power supply hookup?

I have a trailer that has a battery and a solar panel. Obviously, the power is sometimes a problem if the battery drains. I have put an exterior plug on the trailer for a 120v power feed. I can convert the 120v to 12v with an adapter. My question is where to hook the 12v power into my system properly? I have a solar power panel that has voltage into the battery as well as power off that block (not sure what it is called). I have lines coming from the battery to feed the 12v to the system. Do I join them up with teh battery leads? If I join them, will I get 24 volts? Do I have to put in a switch that will completely switch my power source from battery to the 12v power supply? I’m not that experienced with multiple sources. I wondered if there were thoughts on this site?

If it were me, I’d want simple, and simple means keeping the two separate. Either use a “1, 2, OFF” isolator switch to select the power source, OR, plug the shore power into an 120V AC battery charger and just run everything off the battery while it gets charged, sun or not.

Your use case would determine which would be best. If you have access to shore power a lot, I’d go with the first option. But if you mostly boondock, the second would be simple to install and would leave you with a topped-off battery when you left the campground (or your house). Just make sure the total amps that the AC charger plus solar charger are under the limit for the battery.