It may be a bad DC jack.
I know the original poster started this thread some time ago, but I would like to add my experience with this particular error on several machines and what I eventually found to be a fix for them. I personally own an E4300 laptop that started getting the "Please Connect a Dell 65W AC adapter or greater" error about a year ago. It didn't bother me at first because I used the laptop at my desk for the longest time anyways, but the system started to DRAG. Performance is throttled down significantly when it cannot determine the AC adapter. I replaced the Dell with an Acer, but held onto it because I thought one day I'd come back to determinely poke at it.
I have been a computer repair tech for 12 years and have seen so many of these errors occur. With my E4300, I bought a genuine 90 watt adapter. I replaced the battery. I flashed the BIOS. I disabled quick charge in the BIOS. I just couldn't stand to use the laptop with the performance drop.
A post in this thread mentions soldering a chip from within the AC power cord directly to the pin on the DC jack. The E4300 is simple enough to only have a DC Jack that is wired, not soldered, to the board, and after buying $80 worth of adapters, what was one more little component.
It was the DC Jack. Looking at the old, original one, it is in pristine condition. Not a tear or funk in any of the cables, but I guess somewhere hiding under the plastic is a lose or confused cable wiggling around. I created an account here for the sole purpose of mentioning this quirk because I love my E4300 and I hope it might be a somewhat cheap attempt to fix the problem, rather than buying new batteries and AC cords from "official", expensive sources.
And a replacement jack is $5.99 USD online. I have been a tech for a long time and encountered this error dozens of dozens of times. In some cases it is the AC cord. Seldom is it the battery (Battery gives a slightly different error is most cases) Our shop keeps several DC jacks for the most common Dell laptops and I have swapped out and soldered a few dozen. That fixes it about half the time.