"У мене дев'ятнадцять тарілок, але мені потрібна ще одна."
Переклад:I have nineteen plates but I need one more.
Else wouldn't work in this context, else usually means something different, not another of the same thing.
You could say "I have nineteen plates. but I need another one". To use else in the sentence it would need to be more like "I have nineteen plates, but I need something else. I need a fork".