An all-linear approach would be a simple sine wave oscillator, followed by a power amplifier, followed by a step-up transformer. Conceptually, pretty straightforward. IRL, not so much.
There are many choices for the oscillator, determined by the desired harmonic distortion level, frequency accuracy, etc. OK, that one was easy.
The power amplifier has to make 200 W after its own inefficiencies, powered by a single 12 V rail. If we assume the output cannot get closer than 1 V to the rails due to output transistor headroom, that means the output waveform into the transformer is 10 V peak-to-peak, or 5 V peak, or 3.5 Vrms. At 200 W, that's an output current of 56.6 Arms.
But wait, there's more. Because the amplifier output is centered at 6 Vdc rather than GND, it must be AC coupled into the output transformer. Moving 57 A through a capacitor without a significant voltage drop across it requires one gigantic capacitor.
One way to mitigate this is to use a BTL - bridge-tied load - configuration. This requires two linear power amplifiers running 180 degrees out of phase. This doubles the effective voltage across the transformer primary, which halves the primary current. Also, the DC offsets of the two driving signals cancel out each other, so you don't need a coupling capacitor.
Last up, the output transformer. What you can use is a conventional step-down power transformer connected "backwards", with the low voltage secondary driven as the primary. My guess is that no one makes a catalog standard item that will meet the voltage ratio and input current requirements. Also, the 120 Vac output impedance will not be nearly as low as a standard AC outlet. This will affect the output amplitude stability with load changes, as well as any downstream power line filters. Oversizing the transformer will improve this greatly, but a 300-400 W transformer is a biiiig chunk of iron.
