A better way to reduce the ripple (than to increase the capacitance) is to take care that the electrolytic capacitors are low ohmic! I often use this one in switchers

Look at Kais post above http://www.8052.com/forum/read.phtml?id=132527 and you will see that .although the quoted text does not refer to it, he does show a LC filter following the SMPS. IMHO it is sheer folly not to follow a SMPS with a LC filter and today where ferrites abound at a dime a dozen, that should be considered a must. Re the electrolytics, I do not see the need for particular "low ohmic electrolytics" (no I do not advocate ignorance, just I think the need is less dramatic than Kai states) because the 100nF parallels will supply the bursts whicle the "ohmic sluggishness" of the electrolytics is overcome.

Erik