Today I just moved my PC (Asus ROG GRB II) to Ubuntu 18.04 from Win10. It doesn't have its own speakers, so I need to plug in headphones. Although I have 2 different ports (one for headphones, one for mic), in Win10 they always asked me what I wanted to connect (mic, loudspeakers, headphones, etc) in a small window, where I had to check the option "headphones" and click OK; then sound worked.
Ubuntu does not ask what I want to use for sound when I plug my headphones.I looked in pavucontrol output menu: on the first device - I suspect my headphones - I can see sound (orange label changing its length all the time). Does someone know what's wrong and how to fix it?