iPhone USB Charging Adapter: How does it work?

[rayray5884]

Being the owner of many things that charge via USB (iPhone, work Blackberry, girlfriends Pre, PS3 controllers, cameras, etc.) I had the brilliant idea of buying a powered USB hub, plugging that in, and hooking up all my short USB cables to it. Everything would charge without having to leave a computer on, it would be much more convenient, etc.

Problem is the iPhone wouldn't charge. Just about everything else didn't care that their was never a chance of data being exchanged and happily sipped away on the 5.5v that was made available to it. I googled a bit to try and find some way of tricking the phone into charging. Even thought if I hooked up the hub to a computer, let it start charging, and then disconnected it, that might work. It didn't.

So I gave up on the hub months ago. Today whilst perusing Think Geek I found this little guy:

http://www.thinkgeek.com/gadgets/tra...r/b43f/?cpg=ab

Seems like it's the answer to my problem. The solution must be tiny enough to fit into the USB male/female adapter, but I have no idea what it is. So, what does this thing do that I could probably do myself with a spare USB extender? Is their a transistor/resistor/capacitor/some other random tiny piece of electronics that tricks the iPhone? Does anyone know the possible reasoning behind not being able to charge via any powered USB port?

I anxiously await your response as I debate whether or not it's worth it to just purchase this thing for $7.99. Thanks in advance!