Well, sadly not all micro USB's are the same. I don't doubt there is a standard but my example is a Sony e-reader. They will charge off some micro USB chargers and not others (same for their mini ...

Android phones have used various charger types, from Mini-USB to the now-ubiquitous USB-C. Here's a brief history of the cables you've got stuffed in a drawer.

Identify the port in your camera and buy a compatible cable (e.g., mini-usb or micro-usb). It's not a standard connector on either the D7100 or the Coolpix990.