2.5A @5V? I always thought you couldn't get more than 1A out of USB 2.0. I do know that USB 3.0 specs have changed. Realistically though, if I were going to be using even 1A of current for projects, USB wouldn't be my choice of power for fear of ruining something (ie the motherboard). A Power cube would be the way to go (or even a old ATX power supply), as they are cheap. A MC34063 circuit Could give something like the mentioned voltage range and cost almost nothing.