FIDDLY cables, incompatible plugs and sockets, and the many adaptors needed to fit them all together used to be the travellers’ bane. But the USB (Universal Serial Bus) has simplified their life. Most phones and other small gadgets can charge from a simple USB cable plugged into a computer or an adaptor. Some 10 billion of them are already in use. Hotel rooms, aircraft seats, cars and new buildings increasingly come with USB sockets as a standard electrical fitting.