A slightly different take on this transformer requirements issue..
Hammond used to (perhaps they still do) provide a piece of paper with every
transformer, listing part numbers and specs. Included on the paper was a table
for voltage and current factors for basic rectifier/filter circuits: (extract)
Rectifier Filter Voltage Current VA
------------------- ------ ------------------ ---------------- -----------------
Half-wave cap in DCV = ACV * 1.16 DCA = ACA * 0.38 DCVA = ACVA*0.44
Full-wave center tap cap in DCV = ACV * 1.25/2 DCA = ACA * 1 DCVA = ACVA*0.63
Full-wave bridge cap in DCV = ACV * 1.25 DCA = ACA * 0.56 DCVA = ACVA*0.7
AC values are RMS; VA figures I added in.
They don't say precisely how these figures were arrived at, but reality is a
little different than theory (e.g. 1.25 vs 1.414 for the voltage output from
the filter, don't know whether that's reduced due to R losses or an average
with ripple under load).
I take it these values were provided as guidelines, as complete design takes
into account C size, tolerable ripple, etc.
--
TI published "The Voltage Regulator Handbook" in the 70's, which covers a
lot
of design issues for linear power supplies. Even it references a design
procedure from 1943 (Schade graphical techniques) for the rectifier/filter design.