Absolute requirements:
 5VDC at 4.3A.
 9VAC at 9VA unregulated 
  [...trouble making 9VAC from 5VDC...] 
Why not take a 5V 5A supply and adjoin to it a simple transformer from
mains to 9VAC?  (There probably is a reason, but I sure don't see it in
what you wrote.)
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