On those rare occasions when you find that your laptop's USB port doesn't have enough power to power a portable monitor like the ASUS MB169B+ (the thinnest portable monitor you'll find in the February 2018) to power ) then this cable is for you. This allows you to draw power from a second USB port on your PC or your adapter box. Don't skimp and choose a cheaper/shorter cable. Get a cable like this (at least 3 feet long) so you don't struggle with the monitor when you rotate it 90 degrees because the USB port is on the wrong side of the PC! It's well built and works great.