I recently bought a 3.3/5v power supply like this. I'm powering it with a fresh 9 volt battery and 9 volt to barrel connector cable. Right now, it's on 3.3 volt mode, and I have no idea how to switch it to 5 volt mode. All the videos I've seen on how to use it don't describe very well how to change the voltage.
Basically you just put the 2 jumpers on the 5V position (bridge the leftmost 2 pins on both jumpers).