USB hub fails to power ethernet adapter
I am pretty sure this is an issue with macOS Sierra. I had a similar problem with a brand new powered hub (Dyconn PowerHub SuperSpeed 12 Port (10 Data/Charging + 2 Charging Only Ports). I assumed it was a defective hub and replaced it. However, the problem persists with the new hub. I have searched around and there doesn't seem to be systemic issues with that hub, and there are lots of issues with macOS Sierra and USB power management.

Currently I have a powered hard drive and 2 printers connected to the hub, so I don't think anything is drawing power. The devices seem to work - I can print and access the drive, but about every 30-60 secs a "USB Accessory Needs Power" window opens and closes very quickly.

I am running macOS Sierra 10.12.4 on a MacBook Pro 15 mid-2015. From what I have read elsewhere, macOS Sierra has issues with USB management.