Options for Universal Input Power Supply
You really have the only two answers there are: Linear or SMPS. There are some things you can consider though to make you designs more robust regardless of which you choose.

Linear: Designing a Transformer that can take each of those input voltages and output the correct secondary would not be too difficult. You can double wind the input transformer and have it select between 100-120Vrms and 220-240Vrms. Then with the linear regulators you simply allow them to regulate when the lowest rms voltage is present and burn more power then the highest rms voltage is present.







simulate this circuit &ndash; Schematic created using CircuitLab

SMPS:
These are much harder to design. There are more regulations regarding their standards internationally. They are lighter weight.
If you're worried about sensitive electronics, Use a constant switching frequency and then make a notch filter on the output specifically targeting that frequency.