Timebase effect on measuring ripple on SMPS
When looking at power supply ripple it's very important to use good probing technique.  Long ground leads will lead to noise pickup and will give you poor results.

Once you have good probing technique you typically use a 20MHz BW limit on the scope, and set the timebase to view the high frequency ripple.

I usually capture a picture of what the ripple looks like, THEN set the scope for "infinite persistence" which will allow you to get a peak to peak value for the total ripple envelope, e.g. if there is low frequency ripple from poor mains rejection.