So the second PSU has a "Hybrid" and a "Normal" mode switch. What is the difference?
They also mention the hybrid circuit for fan-speed control since it allows for fanless operation at lower loads where noise output reaches the lowest possible level, and there is also a graph showing the fan's speed in both normal and hybrid mode. Finally, Seasonic provides some information on the fan the unit is equipped with. Their favorite San Ace fan may not be so silent at high speed, but it is, without a doubt, of high quality.