The Chinese government requires new mobile phones to use a standard USB plug for charging. But USB can only supply 5 Volts at up to 500 mA. Perhaps another standard could be set for higher power devices, such as laptop computers and cordless battery appliances. At present these require a bewildering array of different plugs using different voltages and polarities. Plugging the wrong adapter can destroy the adapter and/or the appliance.
The leading option for a standard low power supply would be 12 Volts (as used in cars). Another option would be the 42 volts, as agreed by the automotive industry for new accessories and PoweredUSB: 5V (30 watts), 12V (72 watts), and 24 volts (144 watts).
Another option would be the plugs provided on some airline seats, tecnically know as ARINC 628, Part 2 or more commonly called called an "air adapter". These are typically 15 Volt.
Does anyone know if there is a standard plug and voltage in common use?