I have a analog amplifier like device that uses USB for power via a standard USB-A male cable. I also have a variable 0-16v power supply.
My goal is to adjust the volume of the output, by adjusting power to the driver by the variable power supply and wondering if there are any suggestions as to the best way to go about it.
I have looked for a female USB A to power cables but so far haven't found any by a couple search terms. e.g. "usb to pigtails bare wire" UPDATE: I made one using this approach male to female extension, with male cut off, only red and black wires are needed for power which I later tinned and hooked to the powersupply via alligator clips, the data wires I just cut off, i used a sharpie marker to indicate which side is negative on the connector 
My current best thought is to take a USB extension cable and cut off one of the ends, strip the wires and then either use alligator clips to the power supply OR insert a variable resistor between the power output and the amplifier/transducer.
Best Answer
Adafruit sells an adapter, but it won't help you if the device itself can't accept or won't change its behavior with voltages above USB's standard 5 volts.