I should have clarified that I have not seen anything stating Powerfull contains any prohormones or steroid precursors, but its not out of the question for those things to be found in supplements even if they arent on the label...its happened in the past. However, my idea was pure conjecture based on what I had read about your situation.
If you're experiencing greater state of well being, then obviously something is going on - and if you're not experiencing signs of depressed endogenous testosterone production, then its most likely not ocurring.
Its really hard to say whats going on here - its not just DHT which is hard on the hairline, as really all of the reduced metabolites of testosterone, and even testosterone itself to an extent, can be associated with hair loss.
I would still think some sort of hormonal flux is going on that is responsible for this, and its most likely caused by something in the supplements you're taking - I'm definitely interested to see the results of your tests.
Keep us informed!
And betterman...No, I don't believe that the "extra" testosterone helps your hair grow - like I mentioned earlier, to my knowledge testosterone itself can be hard on the hairline especially those who, genetically, are prone and have hair follicles sensitive to the effects of androgens. The hair regrowth which can occur while on propecia is due to the reduced effects of DHT on the hair follicle, unless I'm mistaken.