The MAX471 is an older current sensor which can handle up to 50 Watt, with a maximum of 25 Volts or a current of 3 Amperes. It is officially not supported anymore however there are still many for sale ...

Arduino Power Meter While trying to measure the load of a circuit and having in my future plans to build a Lab PSU (hacking a ATX PSU or something like that) it was my excuse to make this. It's based ...