Using 1:1 Isolation Transformer Before Boost PFC for 450VDC 40W Isolated SMPS Design?

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Question about power supply design...

I've read that the best practice is a power factor controller followed by a flyback inverter for mains isolated AC-DC power supply, but I'm wondering... Could I just put a 1:1 isolation transformer ahead of the PFC and call it good?  I'm looking to make 450VDC at max 40W into the load (maybe 5W at idle).

Any opinions on whether this would or wouldn't work and more importantly whether it would or wouldn't be a good idea?

Any and all insights appreciated.