Power Yoga, as the name might suggest, is a fast-style yoga. It's a derivative of Ashtanga, and it comes from the traditional Ashtanga series, but was modified to break down the rigidity of classic practice.
Whilst it does have a set structure, it allows for the instructor to add their own personality to the class which brings a different feel from your normal Ashtanga. Similar to Ashtanga, it will make your mind calm and soul peaceful, whilst also making your body toned, strong, and controlled.