Laptop Not Chargering

[Sir Lags A Lot]

So for a good while now my laptop has fits with charging. So you know my laptop is a Dell Inspiron 14 5558. Its nothing impressive but its the only thing i can use for gaming. When its running and it needs to be charged and i plug it in, the battery icon will say "plugged in, not charging". But at random moments it charges, wtf. Its really weird and frustrating. But i would be fine if it didn't charge but here's the really annoying part. When it doesn't charge it'll play fallout 4 from the main menu on battery at 60 fps to 15 to 25 fps. Pls Help!

[Sir Lags A Lot]

Oh, and i missed that when it starts up comes up with the bios saying ac adapter wattage cant be determined, system will adjust performance accordingly to power available.