Putting a large capacitive load on a switcher is likely to degrade it's performance, and won't provide any real benefit on a well-designed switcher. Personally, I would stick to linear supplies for steppers or servos, but switchers can be used. and "whacking great caps" are not always a good idea. They should be big enough to provide an acceptable level of ripple, but no more. The Gecko site has lots of good advice for *properly* sizing and spec'ing power supplies for both steppers and servos.
Regards,
Ray L.