No, adjacent angles are not always supplementary. By definition, adjacent angles are two angles that share a common side and a common vertex but do not overlap. Supplementary angles, on the other hand, are two angles whose measures add up to 180 degrees.
While it is true that adjacent angles can be supplementary, it is not a requirement. For instance, if you have two angles that each measure 30 degrees, they are adjacent but their sum is only 60 degrees, which means they are not supplementary. Conversely, two angles that are adjacent can also be supplementary if, for example, one measures 120 degrees and the other measures 60 degrees. In this case, they add up to 180 degrees.
In summary, adjacent angles can be supplementary if their measures add up to 180 degrees, but it is not guaranteed that they will be. Therefore, the statement that adjacent angles are always supplementary is incorrect.