Protein supplements are typically used in conjunction with a proper diet (or as a band-aid to a subpar diet) to increase dietary protein intake.
Some specific types of protein are made for certain scenarios, such as casein protein for a slow-release protein and whey protein for a faster release.
They differ from Amino Acid Supplement as protein supplements will be a non-specific assortment of amino acids in large amounts, whereas Amino Acid supplementation is in lower doses, in isolation, and for specific purposes.
Protein powders can be from either animal sources or plant sources, it is generally advised for vegans and vegetarians to consider protein supplementation due to the chance that their diet may be subpar.