I am building a charger for mobile devices and I want the input to be universal 85-265V and the output to be 5V 2.1A. I have my circuit designed and at the output I am getting 5.7VDC at no load, 5.2V at 0.5A, and 5.0V from 1A to 2.1A. With a cable attached I am getting 5.7 at no load, 5.0V at 0.5A, 4.8V at 1A and 4.6V at 2.1A. I am wondering what the normal USB charging specs are and if I am within spec? I am concerned about the no load voltage and the cable drop voltage.