Read the Oros of the Holy Great Church of Christ on the baptism of converts from the West Signed by Patriarch Cyril of Constantimople, Patriarch Matthew of Alexandria, and Patriarch Parthenois of Jerusalem 1755/56
I tried to find it online, but wasn't able (maybe some else will have a better time at it). In short it says that the baptisms of the heterodox are invalid because "[they] are administered contrary to the tradition of the holy Apostles and divine Fathers, and contrary to the custom and ordinance of the catholic and Apostolic Church".
Only the Orthodox keep the correct form of baptism! Can you really call aspersion baptism? That would like be throwing only a handfull of dirt on a dead body and saying it is sufficiently buried. Is a baptism of less than 3 immersions (or more) as sufficient? Apostolic Canon 50 explicitlyprohibates it, saying 'If a bishop or presbyter conduct an initiation and perform not three immersions, but one immersion-that administered into the Lord's death-let him be defrocked. For the Lord did not say, "Immerse into my death"; but "Go and make all the nations discples, immersing them in the name of the Father, and of the Son, and of the Holy Spirit."'
The best thing I have personally ever read on the subject of convert baptism is I Confess One Baptism... by Father George D. Metallinos.