Not sure how "good" this information is. As a matter if fact, it presents the view of a specific sect of Christians, not Christians in general.
Since Scripture is very clear that Christian baptism is to be in the name of the Father, and of the Son, and of the Holy Ghost (Mt 28:19), we must conclude that when the complete invocation is not stated in the Acts of the Apostles, it is simply giving us a shortened version of the above.
Secondly, while it appears that water baptism "washes" away sins, the reality is that it is symbolic of the washing away of sins. We know from Scripture that it is only the blood of Christ that can wash away our sins (Rev 1:5).
Finally, Paul was indeed baptized by Ananias three days after he was saved (Acts 9:18). Why would this question even arise when Scripture is plain and clear?