White paper I read 20-25 years ago described how those tend to work. Larger power supplies are required to be power factor corrected. They need to draw sinusoidal power in phase with the voltage. To do that they need a power factor correction front end. In the design the paper described what happens is 120VC gets rectified and stepped up to 240DC. Which then feeds a main DC/DC step down inverter.

I think the advantage of stepping up is the filter capacitors are cheaper for the higher voltage. I think because they handle half the current.