The Raspberry Pi 400 uses the same power supply as a Raspberry Pi 4 - a 5.1V 3A USB-C power supply.
Visit our power supply section for our full range of USB-C power supplies different country formats.
Remember - anything less than 5.1V 3A may cause performance and stability issues. You should not attempt to power your Raspberry Pi 400 from a computer USB port - always use dedicated power supplies built specifically for the Raspberry Pi.