You need an adapter that can supply 65W -- sounds like what you have is too low in output.  
Can I charge my Latitude 5290 2-in-1 with a phone charger?  When I plug it in one of the USB-C ports it says "PC Isn't charging. Use the recommended charger ... etc"The same happens if I try to charge with a battery pack.How can I charge it other that with the AC adapter? Thanks
Trying to charge my Latitude 5290 2-in-1 with a USB phone charger.