Bart van Deenan's solution worked for me under Ubuntu 16.10 but under 17.04 it seems to no longer fix the issue and headphones produce no sound.
Dell XPS 15 9550 Ubuntu 17.04 4.10.0-20-generic
Bart van Deenan's solution worked for me under Ubuntu 16.10 but under 17.04 it seems to no longer fix the issue and headphones produce no sound.
Dell XPS 15 9550
Ubuntu 17.04
4.10.0-20-generic