Almost with a doubt the DC jack is the problem. Did the adapter every fit properly? If the system is less than 1 year old that may be covered under warranty and if so call Dell tech support.
I bought a new G16 7620. I find that the adapter keeps falling out of the rear plug. When I say keeps falling out, think 8 times a day, and whenever I move the laptop. It seems to not even be able to plug into the port completely.  Are others thinking it's loose too?
New G16 power adapter falling out