A Newtonian is the same as a Dobsonian. That is, the tube assembly and the optics are identical. Focal length is an issue separate from either of these terms.
What makes the Dobsonian different is the mount. It looks like a lazy susan for the base, and the telescope tilts up and down on side bearings. So by swiveling the base and tilting the scope up and down, you can easily cover the entire night sky.
These are the most popular types of reflector telescope now because almost all of the $$ can be put into the scope and not the mount. You can't photograph with it, but you can get a lot of scope for the money.
Go to Orion's or Meade's home page for a look at some great Dobs.