The power draw by this miner varies a lot over time as we move through the different phases of the CN algo. The Vegas have their Adaptive Voltage and Frequency Scaling (AVFS), which is what you're seeing in action in a very direct way in the video. Afaik, Polaris cards does not have any dynamic realtime scaling, they'll just throttle you in case of a thermal of power limit breach. I'm not an expert in this field though, others here are more knowledgeable, so if you want to know more I'm sure someone else can pitch in.