As the fuse didn't blow I wonder how you are sure the power transformer is bad. How did you test it? Measuring DC resistances can be misleading. Disconnect all the secondaries and power up using a light bulb limiter. If the bulb is bright then you know the transformer is bad.
Smoke from the power switch is likely just and indication that it's dirty and worn out. Time to replace it.
PS: I see the GA20A uses a double pole switch. An worn switch can arc and cause a short L to N or even earth when voltage is applied. Replace or disconnect and bypass for further testing.