How do you wire a transformer for multiple output and amperage?
Do not use a magnetic shunt on a general purpose transformer. It increases the leakage inductance, which is what you want in a microwave oven power supply, but it will increase the output voltage droop when delivering a current.
If you're going to use a rewound MOT for a general purpose power supply, then put a few extra primary turns on. The MOT is designed to be cheap on materials, and be fan-cooled, so it skimps on core iron running it well into saturation, taking a magnetising current far higher than you would want for a normal power supply.
You can arrange to get x1 and x2 voltages from a single winding if you want, but it's less power efficient than having two output windings. The trick is to use a full bridge for the x1 output voltage, and a doubler for the x2 voltage. This arrangement was quite popular when making direct off-line equipment suitable for 120/240 V operation, but has fallen out of favour with the advent of 'universal' power supplies.



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