You dont need to run a step down convertor here in the states. all of the Japanese power supplys work just fine without them. My SC-19 still has its factory or at least factory cert replacment Japanese supply in it and Ive been using the crap out of it since 99/2000 and its never skipped a beat. Sure our ac runs rated too 110 but in reality it never gets close to that. But if you feel better just buy any repop supply for any standard Jamma board from Happ or Peter Chow , but its really not a nescessity at all
The 4 and 6 slots do use a bit more juice than the 1 and 2 slots but even that isnt an issue , so dont sweat it.
Heck Im even running a extra 12V 80mm fan off of mine { which taxes the ps quite a bit } and I still have no issues. Pics in my sig link bye the way.