"Kudos," "well-done," and other words of praise are forms of congratulations, or an expression of approval and acclaim.
Congratulations are expressed for good wishes on a special occasion, not just an accomplishment. For example, you wouldn't tell someone who just had a baby, "Good job on your accomplishment," but you would say, "Congratulations!" If, however, someone says "congratulations!" when you drop your ice cream cone or get a bad grade on your math test, they're probably being sarcastic.