Dell Inspiron 5755 with a 17" display, running windows 10 and the latest BIOS version from Dell(as of 3/2/2017). AC adapter power supply is a 45W, 19.5V, 2.31A, Dell power supply. It works fine and is not damaged, (lite is lit on the brick and proper voltage out verified by using a VOM). When running on battery for a while and the battery low window pops up, I plug in the power supply and immediately get a message "The AC adapter power type cannot be determined. Your system will operate slower and battery will not charge". I ordered and tried another Dell 45W power supply. Same issue. I right clicked the battery icon in the system tray to display the Dell Power Manager. It says my battery is fine, 100% normal. As I unplug and plug in the power supply while the Dell Power Manager is up, I can see the word "charging" displayed in the management window for a bit, but then it disappears. The battery Icon itself shows that the power supply is plugged in as it displays a male electrical plug. If I remove the battery the laptop powers up fine. The BIOS in this machine does not display the charging device information, just that the battery is 100% normal. While in BIOS I hit the F9 key to reset basic bios functions to no avail. I also tried uninstalling the AC adapter and ACPI- compliant control method battery and re-booting to no avail. I can get the original power supply to charge a low battery by continuously unplugging and plugging back in the connector to the laptop. It takes a few tries, but at some point, it says its charging. I can't get the new Dell power supply to supposedly charge the laptop although, I've had it plugged into the laptop for 3.5 hours now and the battery says it's plugged in and the charge level at 100%. I unplugged the new charger from the laptop and let the battery drain down to 84%. I plugged the new power supply back in. Still didn't recognize the AC adapter, but did keep the battery charge at 84% and the battery icon showed it plugged in. So, the laptop knows it's got an AC adapter plugged in to it, but just won't let it charge the battery.
I did not try the power cable yet. I did discover that as long as I keep the original "not recognized" power supply plugged into the laptop, that it stays charged at 100%. It says not charging, but it's doing something. If I try the cable I'll let you know. I think it's the motherboard though.
Thanks for the response - personally I would hate for it to be the motherboard and need to send my wife's laptop in. I do have a ticket open with Dell because the laptop is not very old - just trying to get some educated information.