For many years I subscribed to traditional Pentecostal doctrine that taught that the baptism with the Spirit came after conversion. But after carefully doing exegesis of the specific passages, I discovered that Christian conversion involved the indwelling of the Holy Spirit. What finally convinced me was what Paul said in Galatians - "Having begin with the Spirit, why are you wanting to continue in the flesh?" (my paraphrase). I thought about why Paul said that, because he was clearly speaking about conversion to Christ which was according to faith alone in Christ, and he termed is as "beginning with the Spirit". This showed me that when a person is converted, they receive the Spirit. Then I read an author who asked the question, "How come the Spirit indwells a believer at conversion, then goes away, and comes back to give a second blessing?" I could then see that once the Holy Spirit indwells a person, He is there to stay.
Paul equates having the Holy Spirit as being converted to Christ, and I then conclude that if a person does not have the Spirit indwelling him, he is not converted. Now, don't confuse (as some will, no doubt) that heresy that because of the belief that tongues has to be the evidence of being filled with the Spirit, that one needs to speak in tongues in order to be saved. That is total nonsense, and is actually blaspheming the blood of Christ which is the foundation of our salvation.
What I conclude then is that we receive the Holy Spirit in all His fullness at conversion, and then as we grow in grace and knowledge of God's Word, we learn how to release the power of the Holy Spirit from us, as rivers of living water, to share the gospel - which is the true power of God that causes those who believe the gospel to be born again of the Spirit.
In actual fact, there is no other power than the gospel of Christ preached and share through the working of the Holy Spirit. Paul said it plainly: "I am not ashamed of the gospel of Christ because it is power of God unto salvation to everyone who believes".
This idea that exists among Charismatics that there is a Holy Spirit power that causes people to shake, tremble, jerk, and fall over, is nonsense, and is not the power of the Holy Spirit at all. Those who have those manifestations are like the steam of the locomotive going out through the whistle and not pushing the driving wheels. The real power of the Holy Spirit is the gospel of Christ that is activated in those who believe it, so that they are truly converted to Christ and become new creations in Him.
The best example I know is when Charles Finney got alone with God to really know if Christianity was real, experienced the baptism with the Spirit, got converted to Christ, and as he went back home, met a person on the road, shared the gospel and the guy was converted on the spot. That is the true power of the Spirit; not the waves of glory that came over him, but the immediate conversion of the man he shared the gospel with.