Is this device completely wireless? Unfortunately, I have to buy another stupid Roku with 4K to work with the air display on my MacBook Pro so I can get my work done. Is this device completely wireless? Or does it require a power supply cable?
Yes, and no USB-ethernet adapter will work with it either.
It also requires power (as all CEs do), which is supplied via USB and comes with a USB AC adapter. You may be able to plug it into a USB port in your TV/AVR/PC, if it provides enough power (probably at least 700-800ma in order to be stable enough).