what's the reason for connecting the hub to AC power?
this is a 7 port hub connecting to a laptop
Most USB ports only have 500 milliamps per port, so if you plug in an USB switch and plug in several items to the switch that draw more power than the originating USB port can supply, it will shut down devices plugged in. The AC adapter allows the switch to supply power to each port so it isn't relying on the originating USB port to supply power to all the devices plugged in to the switch.