I have brand new Inspiron 1520.
Battery fully charged, when I unplug the charger from the wall, but let the plug in the Inspiron for a while (let's say a night), when I startup my computer, I get the message "The AC power adapter type cannot be determined. Your system will operate slower and the battery will not charge. Please connect a Dell 90W AC adapter or higher for best system operation" (needless to say that the power adapter IS a Dell 90W...).
Unplugging and replugging the adapter solves the problem.
I have the same message under Windows when I unplug the adapter from the wall, leaving the plug on the computer side while the commuter is running (to go from one room to another for eg.)
I have contacted Dell support, they asked me to reflash the Bios (already done) then, they sent me an new power adapter : same problem... now they are talking about a mainboard replacement !
While Googling for a solution I've seen this is a very common and long term issue on Dell computers.
Are there any people around here that had the same issue and managed to have Dell correct it ?