Dell XPS 15 - 'Power adapter type cannot be determined' error and running incredibly slowly

I have encountered a problem with my laptop - a Dell XPS 15.
 
When the computer turns on, or I insert the charger, the following error message appears:
"The AC power adapter type cannot be determined. Your system will operate slower and
battery will not charge. This problem might be solved by: Ensure the plug is inserted
completely for best system operation. Connect a Dell 130W AC Adapter or higher."
 
I first encountered this problem a few months ago but on occasion, I have managed to
get it working by taking the charger in and out a few times. Though over the last couple of
days, it won't charge at all.
 
I have tried using another charger, which yielded the same results; though it was not the
exact same charger and actually has a lesser power output. I also checked the bios during
start-up, and next to AC Adapter Type was 'Unknown'. Though the charger can power on the
laptop without the battery inserted.
 
Just yesterday, my computer also started operating a lot slower, at an almost unusable
speed and I think this might be related.

So, I'm just looking for suggestions as to what the problem might be and how to solve it. Thanks.