Adjuncts and complements
Adjuncts and complements are different. An adjunct is not necessary, and adds extra information. A complement is necessary in order to complete the meaning:
[S]He [V]put [O]some salt [C]in the soup.
The verb put must have a complement saying where something is put. Without the complement (in the soup), the clause would not be complete. We cannot just say He put some salt.
Adjuncts and postmodifiers in noun phrases
Adjuncts are different from postmodifiers in noun phrases. An adjunct adds extra information to a clause. A postmodifier tells us more about the noun (n):
[S]They [V]’ve closed [N] that restaurant [postmodifier]on Market Street.
on Market Street is a postmodifier. It is part of the object noun phrase. It tells us which restaurant we are talking about.