Power points are awarded according to the number and quality of a member's submissions. Areas & Ranges, Mountains, and Articles are awarded the most power points, followed by Routes and Trip Reports, followed by all other non-Image objects, followed by Images, followed by a fraction of a point for the comments you post to other people's submissions. The precise number of points you receive for any submission is measured by the number and nature of the votes that the specific submission accumulated. Power point levels are updated daily.
Power really comes into play when page score is calculated. Votes from new users with zero power points are not heavily weighed. Meanwhile, votes from valued contributors to SummitPost will figure significantly in the score calculation. As your contributions to SummitPost, and thus your points, increase, the value of your votes, new and old, will count more, even retroactively.
The vote weight number you see on your profile page corresponds to the weight of your vote. The maximum weight your vote can carry is 100%.