This is not a defect. A capacity listed on the packaging is a capacity of the battery inside the Powerbank. The battery has a nominal voltage of 3.7 V while the USB output of the power bank has 5 V. Due to the change in output voltage and heat loss, the real capacity of the Powerbank is proportional to 0.6 - 0.65 times the value of the battery. That means that the Powerbank with reported
This power bank type is equipped with an integrated Lightning adapter hidden inside the power bank itself, just above the charging cable. All you need to do is plug the cable into the visible micro USB connector and pull the adapter out.