Openbabel: Generate random 3D geometry
Random conformer search generates random conformers

Open Babel, like many conformer sampling tools, has a set of common dihedral angles to sample. This minimizes the search space, e.g., only 3-4 likely cases for each rotatable bond.

The RandomConformerSearch method indeed generates conformers using a random sampling of dihedral angles. It then (optionally) runs a force field for some number of steps to minimize any steric clashes. No energies are considered.

If you're finding only one conformer output, that's because you're not using the --writeconformers flag:
http://open-babel.readthedocs.io/en/latest/3DStructureGen/multipleconformers.html