Conor McGregor responded to Floyd Mayweather's insanely fast boxing training video with a clip of his own -- one that showcases his power. 

While Floyd showcased blazing speed and quick footwork, Conor's training video was more focused on power shots ... particularly, a punishing uppercut. 

Everyone keeps saying it's a matchup of speed vs. power (you've heard the "all it takes is one shot from Conor" argument) ... these videos seem to play right into that story line. 

Conor issued a warning to Floyd -- "You've never seen these moves."

We'll see ...