what's the reason for connecting the hub to AC power?
this is a 7 port hub connecting to a laptop
You'll need the AC adapter if you'll be connecting peripherals/accessories that draw extra power. A standard keyboard, mouse, or small peripheral (in my case, a mini music keyboard) draw a smaller amount of power. A larger accessory (in my case, an audio interface box) needs more power than what is coming through the USB port passively. Overall, keep in mind that you're plugging in 7 different units into a single port, so that port's power is being split 7 ways. The AC adapter ensures that all 7 devices will get the power they require.