This project was published by the german magazine ELV about 10 years ago .
Its a switchmode labsupply regulating from 0 to 30 Volt and upto 20 Ampere with voltage and current regulation .
Being a SG3525 fullbridge it can continues deliver 600 Watts at an efficiency upto 90 % .
Only minus is that the article is in German ,but the project is to good not to put it here just for the language .
Being a labsupply its complete with meters based on the icl7106 .http://rapidshare.com/files/216056403/030v-020a_power.pdf
Little note about safety .
For testing they advise to use a 1000 Watt separation transformer .
Always be carefull when working with mainsvoltage ,
(otherwise you might write your next comment without eyebrows