Ian's notes

Most ADSL routers make use of 12V power supplies, providing around 1-1.5A. It’s important to note, though, that this takes into account running the router at maximum capacity on all ports and antennas and supplying power to an external device such as a hard drive. This means that, in practice, routers use considerably less power than the power supply is rated for. I took advantage of this to run my router off of a 5V 2.1A power bank USB port. You can also run this solution off of a laptop USB port.