From memory, but I think USB has 4 pins being power+, power-, data+ and data-, and if you connect the data+ and data- then (some, most, almost but not quite all) devices will assume they are connected to a dedicated charger rather than to a computer which can also do other stuff, and on that basis that they can charge faster by drawing more current than the 500mA limit allowed by the USB spec. Usually the said two pins are connected internally inside the charger, but it would also be possible - I do not know if it is common - to make up a lead that joins them.