If you want to reliably charge your battery, you need a genuine Dell AC adapter of at least the same wattage/amperage as the original. Dell laptops can identify a Dell adapter from a component in the adapter. A third-party adapter will not be identified as genuine Dell, will not power the system to full performance, and may not charge the battery. If a genuine Dell AC adapter that you know is good (tested on another Dell laptop) is not recognized in BIOS, then the next likely suspect is the DC jack. They can be replaced relatively easily for anyone experienced in working inside laptops. (If you had given us your laptop model number, I would have looked up the part for you). If a known-good genuine Dell AC adapter and a new jack won't work, then the fault is likely with the charging circuit on the motherboard, which would normally require replacement of the motherboard. You should also run Dell Diagnostics:Press and hold F12 while booting to enter the One Time Boot Menu, select Diagnostics and press Enter. The Dell Diagnostics will test major hardware components.
So I had a problem where it didn't want to recognize the AC adapter and not charge, I bought a replacement AC adapter not made by dell but it has the needed power (Input: 100-240V - 50/60Hz) (Output: 19.5V). The AC power adapter has since still been seen as unknown. When I connected the charger it still said plugged in and it was not charging, I discovered that if I wiggled the charger a little in the charging port (which is suspiciously very loose)  that it would start charging. I've been doing the same wiggling technique for a few months now and yesterday it decided to not work no matter the angle. My suspicions were that the charging pin inside my laptop was broken or something or the ac power adapter just gave up but I can't figure it out. I am not a computer technician so I apologize if I don't know the name of the parts for my computer I just kind of guessed but I'm sitting here with my laptop at 1%. [IMAGE]  
Plugged in but won't charge, AC adapter unknown.