Both words are grammatically adverbs. I see them quite often but still can not understand which one is more suitable to use.
What exactly is the difference? Can you also create the usage example for both of them in a proper context?
"krom" is not an adverb but a preposition. It cannot stand alone but only in front of a nounish word. If you need to use "krom" in an adverbish way you can turn it into an adverb "krome".
Ni vidis nenion krom grizaj nuboj.
Ni vidis multajn belajn konstruaĵojn kaj krome ni bone manĝis.
But you can also turn "krom" into an adjective "kroma".
Estas bone havi kroman ŝargilon.