Pick up one of these at an industrial auction.
It will give you 120/240 Volts single phase.
Most of these are 6 or 8 KVA with a three cylinder engine.
You will find some with a four cylinder engine rated at 20 KVA/KW.
I own one of each.
The larger auction houses will have larger three phase sets on offer, some trailer mounted, some skid mounted. (Bring your own trailer.)
It is extremely unlikely that you will find a generator that outputs both 208 and 480 at the same time.
You will need a transformer.
Your choice will be influenced by the demand at both low voltage and high voltage.
For example, to drive one 480 Volt motor and a lot of low voltage single phase load, you may choose a single phase generator and use a transformer and VFD to drive the motor.
If your greatest demand is at 480 Volts, look for a 480 Volt generator and use a transformer for the lower voltage loads.
Bill
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Ohm's law
Not just a good idea;
It's the LAW!