Charging problems, please help

Hello,

I have recently had my laptop repaired through Currys.They replaced the battery's and gave me a new charger. The battery's cost a good chunk of my money, as they weren't on insurance.

It has been charging and working fine since I got it back (few weeks), up until about an hour ago. My PC started lagging out of nowhere. I couldn't run websites smoothly, nor run a game. I first restarted my laptop. Didn't work. I checked my pc for updates, then restarted my laptop to update it. After restarting, it came up with a pop- up saying:

"The AC power adapter wattage and type cannot be determined. The battery may not charge

Please connect a DELL 45W AC adapter or greater"

When I plug in my charger, the charging light doesn't stay on. It turns off. The battery icon says that my laptop is charging, but the battery percentage isn't increasing.

I have not rammed the charger into the charging port: I've treated my laptop consciously since I got it back.

Please help me understand what I can do to fix this. I'm upset that my laptop's battery is still having problems.