A
@UnFleshed One said:Oh, ok, all USBs are powered, but 2.5 watts is maximum it can give (per hub?). So I guess USB hubs might fail to deliver enough for devices that operate on the limit...A USB hub with its own power supply should deliver power to all of its ports. A hub without its own power supply can deliver no more than one port's worth of power in total, so if you connect multiple full-load devices to it, only one of them is going to get any power.There's a negotiation protocol involved so that the host can decide which devices to power; only 100mA is guaranteed, and anything above that happens only if the host wants to supply it. A port which never supplies more than the minimum 100mA is considered "unpowered".