There is a large thread on rcgroups that has been going on for a couple years about converting server power supplies for this very purpose. I would search rcgroups for server power supplies, as certain models putting out 13-14V and amperages from 30 up, I wouldn't even bother with a desktop PSU, especially after I read those posts. I believe the originator of the post is in a country, Australia, if memory serves me, that lives on 220V so they were getting 100A, 13-14V servers. It is all diy (which you will be the bulk of my posts), but very doable.