There is a physical current limit, but it's way beyond your 500 mA use. This limit is determined by the size of the relevant PCB traces. Once this threshold is crossed, the dock will become abnormally hot, to the point where the PCB traces will literally burn like an end-of-life tungsten light bulb, plus smoke. Then, GAME OVER !! This phenomenon is only fun when you provoke it on purpose. So, when adding new hardware/gadget/stuff, it's always a good idea to feel if the devices' temperature remain stable. Warning, some devices do get very hot, and it's by design (like a CPU). There are tools to take the temperature from afar to keep your fingers safe.