Fixing the weak swing is the first problem.
Then timing WHEN the head speed contacts the ball is another.
And of course, last and most important, a "power serve" needs more flat and less topspin. It can have topspin, but the swing has to be even faster.
While the toss more into the court is the obvious (yes, I thought that too) first change, I do notice that Roddick and Raonic don't necessarily land too far into the court when crushing huge fast flat first serves. They want to stay back to give themselves time to react to the possible return. Look at some Soderling and DelPo flat serves. Sometimes, not every time, they end up about 2' inside their own baseline, no more. That means the toss can't be too far inside the baseline.