circuit breaker finder doesn't work with isolated AC?

[ledtester]

I was playing around with a Sperry CS550A circuit breaker finder:

https://www.sperryinstruments.com/en/p/CS550A/Sperry-Instruments-CS550A-Circuit

and I found that if I plugged the transmitter into my Heathkit IP 5220 Variable Isolated Power Supply the receiver didn't pick up the transmitter's signal.

The emitted tone from the transmitter was a slightly lower frequency than you would hear from a regular wall outlet, but even going through the "calibration" procedure for the receiver didn't work.

The transmitter only has two prongs - I'm wondering what's going on...

Operating instructions for the CS550A:

https://www.sperryinstruments.com/-/media/inriver/CS550A_USE.pdf?modified=20200714143629

[Manul]

I imagine, this device injects a frequency which is quite high, like in kHz or 10s of kHz range. In that case, it is expected that signal does not pass very well through a mains transformer, especially when the rest of circuit (mains power line) is quite low impedance, it simply gets attenuated too much.