The invention relates to an interface device for supplying power to a variable number of loads, which are configured to be coupled to the interface device by means of a supply line and which are configured to communicate with the interface device, to a system comprising such interface device and one or more loads, to a corresponding method for supplying power and to a corresponding software product. A particular feature of the present invention is that the interface device functions as an intermediate between an USB power source and the loads connected to the interface device by supplying power while being flexible to both sides, i.e. to the supplying side as well as to the load side, in allowing for a flexible number of loads to be coupled to the interface device (i.e. to be supplied by the interface device with power) and in also providing a negotiation with the power supply depending on the necessary power.