Trailing Socket with USB Ports

What are the USB sockets connected to? or is this just for 5V power?

Max length of a USB cable is only a few metres (5, I think) before the data signal degrades too much. You can get longer by daisy-chaining hubs, and there are USB extension leads which consist of a 1-port hub with a 5m lead.

I thought it could be used for charging things like mobile phone, spare battery and stuff like that. Maybe not a good idea though. Thanks for the info.

article,

Just plug one of these [see below] into a standard 13A extension cable.

Plenty of other versions available all over the place.

Or have a look at this search

which does have extension cables with USB built-in and other products.

In article , Stephen2 writes

They're called USB repeaters. You can daisy-chain up to five of them.