Charging dock not functioning properly

This is the 2nd dock I have bought in less tha. A year. The 1st one didn’t function at all. This one will fully charge and initially would work when you slap on the watch without the USB cord connected (which is what. It’s supposed to do). Of late this doesn’t work unless I have the USB connected…only then will it continue charging once I remove the USB. So it requires the USB to be connected to initiate charging. (The dock will be fully charged)