supererogatory vs excess

supererogatory is not a noun while excess is a noun.

Word	Noun	Adjective	Verb	Adverb
supererogatory	No	Yes	No	No
excess	Yes	Yes	No	No

As adjectives, supererogatory and excess are synonyms defined as:

Other synonyms of supererogatory include extra, redundant, spare, superfluous, supernumerary, surplus.

supererogatory (noun)	excess (noun)
	excessive indulgence
	immoderation as a consequence of going beyond sufficient or permitted limits
	a quantity much larger than is needed
	the state of being more than full

supererogatory (adjective)	excess (adjective)
more than is needed, desired, or required	more than is needed, desired, or required