I have a Dell Inspiron 14 3000 Series. I just installed Ubuntu 18.04 dual booted with Windows 10.
The output of the speakers and headphones work just fine when booted to Windows 10, but when I boot into Ubuntu, the output of the speaker works while the headphones do not.
Pavucontrol shows sound from Rythmbox and that the headphone output is at 100%. I assume this means the headphones are being detected.
The headphones do work with other devices.
This question was asked more than one times before me on this site.