I made a mistake, it uses 0.5W not 5W ;)
This router is standardly powered via USB at 5V. The voltage regulator inside is unknown, but its input voltage should be at least between 3.7V - 6V, possibly 8V. Maximum current draw at 5V is 185mA (OpenWrt boot), average current draw with WiFi at 18dBm is 100mA, without WiFi 80mA. Hence the average router power consumption is 0.5W, which is incredibly low.
Power consumption will be higher if a USB device is attached to its USB port!