Go into Setup (f2 at powerup).  Does the system sense the power output of the AC adapter?  If it does, the issue is probably the battery.  If it does not, the problem is with the adapter, the port or the system board.  
Bought the Inspiron 16 plus one year ago. Using it with a WD19TB dock connected most of the time, otherwise with AC charger connected. Some weeks ago I let the laptop run on battery until it reached about 50 %. Since then I can't charge the battery full again, no matter if using the Thunderbolt dock or the (original 130 W) AC charger. It sits at the same level where I left it (52 %). Doesn't discharge more, doesn't charge over that level. Any experiences like mine, solutions?
Battery won't charge