usb hub power adapter question

[ruffblaza]

i bought a 4 port usb hub today and in the back it has a usb male to usb male connection, and it also has a slot for dc 5.0v but i don't get what is the difference cause the usb hub works with out the adapter and straight with usb male cable so what is the power adapter for? does it give more power or something? better transfer rates?

 

[hunter315]

The USB cable into the adapter only provides 500 mA of current, this is enough to run the adapter and a few USB 1.0 devices that use 100 mA each, but if you try to run 4 USB 2.0 devices each needing 500 mA you will be short, that is what the DC adapter is for.