I think my explanation as what you quoted is pretty clear but dudelove has given more additional info for you to digest if you still don get it
The junior is good cos its small, compact and affordable. just dont expect it to power pedals with really high MA consumption (like a Moog for instance) cos each of its outputs puts out only around 120 ma. Its great for small pedalboard users (im using a pt junior with about 11 pedals on it) dosent take up too much space and costs much less then a voodoo lab pp2+.
Feedback, try running your bulldog and your tubescreamer from the same ouput. I chain all my dirt and boost pedals off one output (im running 11 pedals in total off one fuel tank jr) and i get no noise. that includes a 2 delays, a chorus, trem and phaser. Try to run your dirt, delays and modulations in separate isolated groups.