Think I should say that if you choose the top pic Jonathan drew you will be getting double the voltage of the 2 secondery ouput ratings IE: 2x24=48V but only half the rated Amps of both seconderys but if you wire have 48V seconderys and wire parallel you get the same 48V but double the amps.

No difference really has lower voltage seconderys have higher amps, roughly double, if the higher seconderys are double the voltage.!! . . . So 2 x 24Vac 12A seconderys can either give 48V @ 12A wired series or 24V @ 24A wired parallel. . . . So obviously 2 x 48Vac 6A seconderys wired parallel will give 48Vac @ 12A.

The 48Vac when rectified to DC will give roughly 68V IE: 48Vac x 1.4 = 67.2Vdc

Heres a pic of one (Big one) wired in parallel using 4 x 4700uf caps.!! ( Ignore the chocy block on the input that was a temp bodge.!) Click image for larger version. 

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Has you can see nothing too it. . Simplizzzzz.