power couple vs mates

power couple and mates both are nouns.

Word	Noun	Adjective	Verb	Adverb
power couple	Yes	No	No	No
mates	Yes	No	No	No

As nouns, mates is a hypernym of power couple; that is, mates is a word with a broader meaning than power couple:

power couple: a couple both of whom have high-powered careers or are politically influential
mates: a pair of people who live together

Other hypernyms of power couple include couple, match.

power couple (noun)	mates (noun)
a couple both of whom have high-powered careers or are politically influential	a pair of people who live together