You have bought a power bank and are wondering if it really measures up to the advertised Capacity? Check with this Power Meter. You can connect it to any USB Power Source like your Power Bank. It will Show you the Output Voltage of the Power Bank - This should be 5V On the USB Female side you connect your Load. You can then see the Current that the Device Consumes. Leave it on for a while and it can give you an indication of the Power Consumed. This is also the Power delivered by the source (Could be your Power Bank) It measures Voltage & Current - Power = Voltage x Current (For DC Voltages like this one) The Total Energy that can be delivered by your Power Bank = The Capacity of your Power Bank. Energy (Or Capacity) is the ability for the Power Bank to give X Watts for T Time before it runs out of juice. Hence TIME is the factor that comes into play to measure the Total Energy that can be delivered by your Power Bank or The Capacity of your Power Bank Capa...