The ppa that I linked to in my post about installing the kernel fixes by Kamal Mostafa has moved to a Canonical server. Please update your Dell XPS laptop to get the latest fixes.
Type the following lines into your terminal one at a time, hitting enter after each one to update your system:
sudo apt-get-repository ppa:canonical-hwe-team/sputnik-kernel
sudo apt-get update
This will start the updater program and get you all the latest fixes from Canonical.