The "not powered" or "unpowered" issue with Xbox 360 Kinect is caused by a bug in the Kinect for Windows driver when used on Windows 10.

Sometimes, when plugging in an Xbox 360 Kinect or Kinect for Windows V1. The driver may initialize the device wrong, and one or more of the sub-devices of the Kinect will appear driver-less until updated.

To fix it:

What if I didn't see anything in Other Devices?

In this case, there's a strong chance that your adapter is faulty or broken. Over on the KinectToVR Discord, we've had anecdotal evidence suggesting that USB/Power adapters bought through Amazon sellers are more prone to breaking or being dead on arrival. So we recommend if possible buying elsewhere like Ebay.

Usually the first or second result here should be fine. (US)

How to fix (video version)