RS universal rectifier transformer secondary voltages
They add up to 40V. 

So get out your multimeter and find out if they are isolated windings or taps on a single winding. If they are isolated windings you need to link them together with the correct phase so they add and don't buck. 

Isolated windings would be very flexible, if so you could get (say) 11V by using 9+3-1. Nice bit of kit.