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> The primary chops up the high-voltage DC from the PFC circuit and feeds it into the transformer.

It chops it up to AC for the transformer.

Ah, this makes sense. Do you know how the "chopping it up into AC"works?

I'm no expert so may be corrected, but I assume just an inverter https://en.wikipedia.org/wiki/Power_inverter

This transformer would be a flyback transformer therefore doesn't need to be driven by anything so hard-to-generate as a sine wave. It can be driven by a "switch" (MOSFET) at it's primary which is connected to DC.

https://en.wikipedia.org/wiki/Flyback_transformer#Operation_...

All switching power supplies (hence the name) are driven by either full-on or full-off ("switching") transistors. A "flyback" topology is only one of many possible ways to build a switching power supply, but as it's the simplest, it's the most common in low power supplies.

See the Switch−Mode Power Supply Reference Manual from ON Semiconductor for info on all the other possible ways to build a switching power supply.

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