I assume the USB port complies with the standards. From an article
In terms of current capability, the USB 2.0 specification calls for 1 to 5 unit loads as the maximum capability of a USB port. One unit load is defined as 100mA, and whether the port can supply one or five unit loads depends on the port type. Low-power (100mA) ports are hub-based USB ports, whereas high-power (500mA) ports are host-based USB ports.
Today's higher-current devices (phones, tablets, etc) draw more current in operation than a 500ma source can provide.