MacBook Pro Discharging Under Heavy Load?

I was recently doing a good bit of work in Final Cut Pro on my MacBook Pro (with TouchBar) and the system was running on all cores. The weird part was that my battery was slowly discharging while plugged in.. How the heck?

I am using the Apple 87W Charger and Apple USB-C power cable, so not an issue with third party power products.

Because this seemed like a MAJOR issue since it’s a “Pro” machine, I wanted to see if I could figure out what was going on.

After a little bit of investigation, I think I know what is going on! (at least in my scenario)

When looking at the System Information, I noticed that it said I was only getting 55W. Why would this be? Well, it turns out to be the Apple USB-C Digital AV Multiport Adapter I believe.

Charging MacBook Pro through the Apple USB-C Digital AV Multiport Adapter:

Charging connected directly to MacBook Pro:

So, for whatever reason, the adapter does not allow the full 87W through and knocks it down to 55W, and a MacBook Pro running at 100% uses more than the 55W provided. Kind of a bummer, but not the end of the world by any means.

Is this happening to you? Do I have a defective adapter?

UPDATES 2017-04-03

1. A few questions/answers on the apple.com shop pages talking about this adapter only providing 55W. This looks to be true for the VGA version as well. Furthermore this would most likely be the same issue if you use one of the new LG UltraFine 4K or LG UltraFine 5K displays as they only provide 60W for charging.

2. A friend of mine also contacted me and let me know that this adapter does indeed only provide 55W of power to pass through.