You could also just use one of those cheap USB power/voltage monitors as the author does. Obviously a cable alone should not be drawing power. Maybe an innovat

You could also just use one of those cheap USB power/voltage monitors as the author does. Obviously a cable alone should not be drawing power. Maybe an innovative company could add warnings for USB ports that draw power but have no recognized device. For the advanced ports with charging support and so on they should have power monitoring already.