Also, the official trouble shooting advice from https://support.microsoft.com/en-us/help/402346... states:
If your Surface isn't charging while connected to Surface Dock
Here are a few things to check:
•Check your power supply. Make sure that all the cords are securely connected and the LED indicator light on the Surface Dock is lit. Check your power strip if you’re using one. Try plugging something else into your power outlet to make sure it’s working properly.
•Remove the Surface Connector from your Surface, turn the connector over 180 degrees, and plug it in again. Make sure that the connection is secure and the indicator light is on.
•If you have accessories that draw power from your Surface Dock or Surface, remove them and see if your Surface charges.
•If you’re still having problems, try resetting the power by unplugging your Surface Dock from the power outlet and plugging it back in.