It really does seem to be a power issue. Do you have other phones that can output to a display? You can test that.
Am I right that you also use a portable monitor? Even with a separate power supply to it and the dock, the flicker still happens?
In my experience, sometimes the sequence of connecting the ports may change the behavior or docks and such. I didn't experience the same issue of flickering but I had some other strange behavior with my adapter when connecting the power cable. The same with my portable monitor. I need to connect my phone first then the power to the monitor so that touch would work, otherwise, only the display output works but not the external touch input.