Had 3 problems at once:  bad cmos battery, bad main battery, and damaged power plug.   The power jack has 3 pins encased in a phenolic ring.  Ring was gone so no guarantee that all 3 pins were getting power at the same time.   Still says power adapter type unknown so I turned off the message.  
When I plug in the power adapter,  I  first get a white light and 3 blinks of amber after that from the light next to the plug.  Is that very low battery or maybe a bad battery?   The laptop comes on just for a few seconds but has a black screen and the caps lock light is lit.  I'm sure the power adapter is good.   Thanks! 
Latitude 3590 blinking amber light 3 times