Wireless charger doesn't work with engine running
 

I bought a wireless charging cradle for my phone. I have it plugged into the DC 12v port above the shifter. When the car is in AC or ON with the engine off, it works and chargers my phone. But when I turn on the engine, it stops charging my phone and the cradle singles that there's an error. I know there is still power going to the cradle because the led is blinking. What changes with the 12v port between the engine being on vs off?