One of three things is faulty: The AC adapter, The DC jack,  or the system board. Replace in that order until the problem disappears.  
August 22, 2021 HI I should tell you this issue I have had once this year When my laptop battery was at 6% then I plugged in the ac adaptor into my laptop to charge the battery the number stayed at 6% for quiet a while. So then I left the ac adaptor plugged into the laptop and restarted the laptop. Then I got a message saying: Warning the ac adaptor that is plugged in is not determined and the battery may not charge? What does this mean.So then I restarted the laptop and the same message came up so I logged into the laptop a second time and let the battery go from 6% right down to 0% and then I let the laptop shut down  completely. Then I re plugged the Ac adaptor  back into the laptop and everything is working fine now the battery is charging normally and when I restarted the laptop no warning came up at all. This has happed one other time but I resolved it by doing the above resolution.I got the lasted version of the Bios from the dell.com/support website. version of lasted Bios update is: 1.7.0, 1.7.0Date of update, is: August 17, 2021 I should say that this is the same  Ac Adaptor that came with this new laptop.  The adaptor has no damage done to it. The photos are in this discussion [IMAGE][IMAGE][IMAGE][IMAGE]
Inspiron 7706 2-in-1, AC adapter undetermined and my battery may not charge