What power is going in or out of a USB-C port? How do I tell how power is moving through my MacBook Pro's USB-C ports? My shiny new MacBook Pro (15", 2016), comes with four USB-C ports.

Sometimes power comes in through one of these ports, as when I charge the machine from Apple's included official 87 W power adapter, or another power adapter. Sometimes power goes out through these ports, as when I use them to power my iPhone or an external accessory like a hard drive.

Does macOS provide any tool that can tell me the net flow of power through every one of these ports? Or is there a third-party application which can do so? The benefit of this is it would let me manage my battery better, and also understand if cables, hubs, and power adapters are performing as intended.

The closest thing I can find is to go About This Mac / Overview / System Report / USB, where I see three fields: Current Available, Current Required, and Extra Operating Current. I don't quite understand what these fields mean. Also, they purport to describe current (in milliamps), rather than power (in watts). Without knowing the voltage I cannot know the flow of power, and my understanding is that voltage does indeed vary on USB-C power circuits.
Find at this article for more details regarding USB-C in MacBook.

https://support.apple.com/en-gb/HT204360