Can a isolation transformer be beneficial when coupled with a lab linear power supply?
There will be about 100 pF capacitance between primary and secondary of the transformer.
At 60Hz, that is 10Billion ohms / (2 * pi * 60) = 10,000,000,000 / 377 ~~25,000,000 ohms.
Now 25 Megaohms is 40 nanoAmperes per volt.
At 200 volts peak (actually 160, but lets use easy math), the current is 8 microAmps.
That 8 microAmps will explore ALL possible paths in finding a path back home.
If you have sensitive circuitry, that constant 60Hz buzzing may bother you.