How do planet adjacency effects work?

As far as I'm aware, the only buildings with adjacency bonuses are the Planetary Capital line of buildings (and their upgrades) starting from the Planetary Administration (after upgrading the Reassembled Ship Shelter).

In this case, as per their descriptions, they provide +1/+2/+3 to production of adjacent Minerals, Energy, and Food. Sorry, scientists!

These 3 are listed on the Stellaris Wiki, and there don't appear to be any others.

According to this dev article,

Buildings can also be constructed in tiles, and they often have adjacency bonuses for the resource they are producing. Therefore it will be advantageous to construct your power plants in proximity to each other, to achieve optimal efficiency.

so the adjacency bonus should come from buildings that produce the same resource in an adjacent tile.