The organisation behind the USB standard has announced that a new standard of the interface has been finalized. The new specification is of the "Power Delivery" type, which describes how attached devices are powered. The new standard allows for a major improvent, the drawback being the requirement of special cabling.
The new standard reportedly allows USB to delivers up to 100 watts, sufficient to power notebooks, as well as external hard disks, printers and other devices. While the current standard has a maximum voltage of 5V, with a current of 5 Amps, most cables only support up to 0.9 Amps, which could be significantly increased by the new standard.The full specifications of the new USB standard can be downloaded here.