You might also consider a 7.5V and a couple 15V switching supplies
adjusted up to +8 and +16. This is what Grant Stockley does in his
Altair 680b replicas. The 7.5V units are little more rare but you start
to see them at 100W and higher even at places like Marlin P Jones.
eg,
http://www.mpja.com/prodinfo.asp?number=16012+PS
--
Chris Elmquist