The filter capacitors can vary widely in value depending upon the operating frequency of the chopper, the design current, and so on.
Or did you mean the filter capacitors incorporated on the AC input to reduce interference being sent back down the mains?
You might find this link of interest. It contains many
more links to articles on switched-mode supplies: http://www.epanorama.net/links/psu_switching.html
[This message has been edited by pauluk (edited 08-19-2003).]