PC Power Supply Design Question

[larrymoencurly]

Why does almost every AT and ATX power supply have at least two inverter transformers, one to step the 120VAC to a safe voltage, and at least one more to provide the output voltages? Why can't they make PC supplies like some other supplies that accomplish everything, including isolation, with just one transformer?

Here's a schematic of an ATX supply.

 

[BartManInNZ]

The main reason from what I know is the current and voltage requirements for a PC are such that any different designs of power supply from Switch Mode would be a lot bigger to implement.

Sure you could design a toroid transformer based PSU but where would you put that?