I'd love to see somebody sell an old-fashioned motor-generator set for generating absolutely pure sine-wave current from a noisy input. Give it a really heavy flywheel and maybe some complicated flexible interconnect between motor and generator, to remove any effects of the input power. Or, even better, have the motor crank up some sort of mechanical/hydraulic/pneumatic power storage, then switch off to let the generator run for an hour or so.
Yeah I mentioned it in my other comment, spinning flywheel generator with a motor on one side and generator on the other would work well here too filter out any noise.
Some datacenters have these attached to their generators to avoid the need for huge battery banks. They can actually support several megawatts. They spin constantly at the motor's rpm with a clutch that engaged when the input power is lost. This instantly jump starts the generator, at the grid's phase, and prevents
