The certified translation implies that the translation of the official document (passport, birth certificate) was conducted by a professional translator who is employed by the translation agency.
The agency certifies the document (places a stamp) thus gives it a legal power.
The notarized translation is the translation that was made by the individual translator (freelancer), or even by the owner of the document, and then signed and verified by the notary.
There is no need to notarize the certified translation.