Have a 9930 as well as a Storm, when using a non-RIM car adapter, get message that the battery will not be charged. Works fine with a RIM car charger. At first I thought it was the wattage being supplied was too low, just tried a car adapter, USB to Micro, 1.0A and 2.1A, get same message on both USB jacks. Any reason Blackberry not compatible with after-market adapters? Any fix?

The fix is use the BB car charger.

Many Verizon devices require the carrier supplied charger. Been that way for a long time. Don't know why.

My thought is the charging cable may allow the BB to detect the connection to the USB port by seeing the data pins. The RIM charger may have either a loop or other way of telling the BB its connected and therefore allow the BB to charge. I would suspect aftermarket chargers may not be able to do this.
Only my thought.
I included the document on charging characteristics



KB18223-Charging behavior of the BlackBerry smartphone

This was definitely the case with Nokia devices in their original Micro USB chargers as well as their old headsets.