I realize this is an old thread, but, you might want to look at something called Ferroresonant transformers or also called CVT Constant Voltage Transformer.
What these are is a transformer with an additional winding and a capacitor that forms a resonant tank circuit at your line frequency.
they have many advantages,
good regulation handling +/- 40%+ input voltage change.
the output is a clean sinewave due to the resonant circuit.
good noise and spike isolation and electrical isolation.
Simple design
Self-regulating
handles non-linear and high crest factor loads well.
disadvantages are
they are bulky/heavy compared to other line regulation or just standard 1:1 transformer
there noisy due to operating at resonance.
they are inefficient but efficiency goes up with the load.
very sensitive to line frequency changes (not good to put on a generator for example)
