Modern personal computers always use switched-mode power supplies, which has both efficiency advantages and makes designing for multiple voltage inputs easier. This means that most PSUs can operate in different countries where the power input might change. In the UK, the voltage is 240V 50Hz, whereas in the USA the voltage is 120V 60Hz, and in Australia it is 230V 50Hz. Some power supplies have a manual switch for selecting input voltage, while others automatically adapt to the mains voltage.