AC power adapter wattage and type cannot be determined - battery won't charge

Solution 1:

The warning signal was from BIOS and had nothing to do with Ubuntu. Turns out there was something wrong with my charger making it unable to charge the battery. Replacing the charger with a new one fixed the problem and the battery now charges as it should.

Solution 2:

Going back for some time the OEM 19.5 volt Dell chargers actually have 3 different "pins" even though it appears that there are only 2 connections. There is the outer shell connection, an inner shell connection, and a small pin in the center. The outer and inner shell connections are the power circuit. The small pin is a sense circuit.

When Dell reduced the size of the charger connector it made the sense circuit contacts even smaller and IMO less reliable. (Look at how much larger the older Dell plugs were.) I think the "power, no charge" problems are most often a result of the sense pin not conducting properly. The problem can be in the computer female or the charger male section. If you are lucky, it will be the charger male connector and not the computer side.