modding at/atx PSU for tec psu

[chris4521]

Im looking for a cheap tec PSU. probably to run a 226W tec on a dd maze3. i understand i wont get full power with a modded PSU, but can anyone show me a guide on how i would do this?
i've got some old at/atx PSU's laying around (around 300/350w) that i'd like to put to work in my system.

thanks in advance.