great write up on these 5v-3.3v breadboard power supplies. Very little documentation is available online. It is one of those figure it out yourself add-ons. You get dual output that is selected via the jumpers. Either 5v-5v or 3.3-3.3 or any combination of the two.
One bit of caution is that if you reverse it on the breadboard your + & - rails will also be reversed. Pictures are below.
You can feed this 5v dc via USB or do what did and feed it 9v dc @ 750mah via the barrel connection. (tip positive sleeve negative)
This is the correct way