The Schafer Push was first performed by Karl Schafer, two time Olympic Champion (1932&36). He invented the push for the school figures, backward outside loops. 
The Schafer Push is a challenging push to get maximum power. I like to introduce the push by starting from a stand still, like the way we did in the days figures. This inspires the use of more force into the ice.  To achieve maximum power, the feet start perpendicular to each other. If a skater tries a perpendicular push during Backward Cross Strokes and Inside Choctaw, deeper edges, and more power would be the result.
Also note that Hockey Player can also benefit from practicing a Schafer Push to gain power in pivots.
The video shows the push from a stand still and then as Backward Cross Strokes, and an Inside Choctaw.