Calculating the smoothing capacitor for a power supply
Conceptually, if t is reduced (the AAC signal is of higher frequency) the time the capacitor ISS discharged over is reduced, thus ripple reduced.

That is all switching mode power supply is all about (almost), reducing the ripple by charging up a small capacitor at higher and higher frequencies.

Edit: you can think of the voltage as water level in a bucket with a hole on its bottom. The more frequently you can fill thee bucket, the less fluctuation in thee water level you see in the bucket.