a powered USB hub is for USB devices that draw a significant voltage/current from the USB port that the computer/laptop cannot handle. I finally ran into trouble were i have 3 wifi devices at the end of a 30' USB cable (2 x 15' cables). the power hungry TL-WN722N wireless network adapter made the laptop BSD eventually when running by itself with inssider and couldnt even be detected when it was plugged in with the other 2 wifi network devices. the laptop has a powered USB port, but apparently it was only enough power to use either of the other 2 weaker wifi network adapters. a powered USB hub remedied the lack of USB power for using all 3 wifi network devices at the same time on the single USB cable.
a USB active/repeater extension cable is to 'repeat' the data when you go over 30' and up to 90' where if you have a longer then 90' USB length it may or may not work at all.