Many CrossFit types dabble in pre-workout to get mentally (or physically?) prepped for heavy 1RM lifts. The attached studies surprisingly demonstrate that the caffeine laden supplement has no impact on 1RM bench press, leg press, vertical jump or medicine ball put (MBP). These are all measures of 1RM power output.
The supplement did however, measurably improve Anearobic capacity and delayed muscle fatigue in submaximal bench press, leg press, and in the Wingate Anaerobic Power Test, and intermittent anaerobic running capacity. Check the linked studies. While they lack a large sample size, 13 is considered to be large enough to yield reliable information and they have the proper controls in place.
Study Link #1– assault-improves-muscular-endurance
Study Link #2– assault-study