Anyone else bothered that they do not specify the energy in watt-hour? Back when USB was 5V it was pretty easy to do the conversion from Ah, how does it work now that USB can negotiate voltage dynamically?
Usually they just multiply the number of cells with their "rated" mAh-value, but who knows what their cutoff voltage is. Also you need to integrate over the voltage (which keeps falling during discharge) and the discharge graph also depends on how much power you draw. Then the 4.2V=>5V (or 9..19V for USB PD) conversion losses are also not counted.