Since I upgraded from Ubuntu 15.10 to Ubuntu 16.04 LTS on my Dell XPS 9350, suspend is broken. When closing my lid the laptop will suspend, but resuming fails and it reboots. I tried pm-suspend and tried resuming, resuming failed and the laptop rebooted. I got the following errors when I got back into Ubuntu. The odd thing in my opinion is that it claims the kernel is not an official ubuntu package. Either way my Linux knowledge is not sufficient to know what's going wrong here.
EDIT: I just tried installing kernel 4.4.8 which should fix some things, but it did not fix this problem. By now I also tried 4.4.9 and 4.6 RC7. None of them fixed it for me.
Best Answer
I had this same problem on an XPS 15 9550. The only thing that worked for me was going into the bios and turning on "Block Sleep" under power options. This apparently turns off Intel Rapid Start and sleep (state 3). So technically the machine doesn't hibernate / suspend (state 3), but it does go to a higher sleep state when closing the lid / opening / power button and comes back fine. Seems like until the issue is addressed in the kernel, or driver this may be the only option and is the only thing that worked in my case.
EDIT: This script worked for me and I was able to turn off Block Sleep in bios! Sleep / suspend now works on my ubuntu 16.04: https://ubuntuforums.org/showthread.php?t=2317843&page=11