While charging my phone (a Samsung Galaxy S5) with a power bank that displays the power output with 0.1 W resolution, I turned the screen on. To my surprise, the power pulled by the phone went from 7.1 W to 5.0 W instantly.
I repeated the experiment many times. Screen on, 5.0 W. Screen off, 7.0 W.
I would have expected the phone to either pull more power to both charge at full speed and power the sceeen, or to pull the same amount, and simply charge the battery at a lower rate.
But I find the drop in power when turning on the screen counter-intuitive.
Does anyone know why this would happen?