Call me "Stupid" or Stu. - Mavic Pro Controllers.

[Felix le Chat]

When you say "An external Power source" where does this plug in, the charging port or the USB port underneath?
I wonder what the chances of a Universal plug and socket are in the future? Life would be so much easier. It seems the companies making them are only interested in making life darned awkward plus making more money of course. They design a new socket and we all have to buy the new cables sporting the new plug to suit.
Then along comes DJI and decides to make a socket we have a 50% chance of wrecking, which in turn makes the controller it's fitted to useless.

Actually that 50% is more like 85% when "Murphy's Law" is taken into account. I say that from personal experience, Murphy lives at my house.

The external power source (10,000mAh power bank) would plug into the MICRO USB port on the left sidewall of the controller. The full sized female USB socket between the clamshell handles is an auxiliary video out only.

I use this kind of setup when I'm out in the field and want to make sure there's enough charge in the controller to run through five flight batteries one after the other. If you're interested, I'll shoot a few stills of the assembly to show you how it's done.

 

[Yorkshire_Pud]

The external power source (10,000mAh power bank) would plug into the MICRO USB port on the left sidewall of the controller. The full sized female USB socket between the clamshell handles is an auxiliary video out only.

I use this kind of setup when I'm out in the field and want to make sure there's enough charge in the controller to run through five flight batteries one after the other. If you're interested, I'll shoot a few stills of the assembly to show you how it's done.

For clarity, are you saying that the controller will take charge through the side port and that the big USB socket will output video etc. whilst the controller is being charged in that way ?
If so, COOL, that might be handier than using a splitter cable.