Not all charging cables for USB devices are created equal. Charging cables will have their own unique resistance that create voltage drops and thus reduce the power (Wattage) available to charge the internal batteries of USB devices such as phones, power banks, watches, and headlamps. Generally, the longer the cable and the thinner the wires, the larger the power loss created by the cable.

This video shows how an inexpensive USB Load Tester can be used to compare charging cables, so that one can select the charging cable that has the highest fidelity and creates the least power loss. Perhaps a general rule of thumb when a USB Load Tester is not available is to select the shortest, thickest and heaviest cable to use for charging. However, compromises may need to be made based on convenience and cost.