WorkingAtHome said:
I assume I am missing something...
A 800VA transformer with primary connected but secondary not connected consumes about 400VA of reactive power. The corresponding current generates a rather strong low frequency electromagnetic field (H field). No mains filter can filter that.
So, mains cable geometry counts for sure. One can find enough info in EMC books to evaluate "how much".
A transformer has also inter-winding capacitance (it can be measured approximatively with a multimeter). At least this provides a path for high frequency currents (example: diode switch-off noise if no snubber or capacitor across rectifier bridge). This HF current must return to its emitter else it won't go anywhere. For exemple, the current loop may pass through mains, another audio device, and interconnects. This is quite a huge loop, so it's quite susceptible to be noisy. Past a frequency, any cable reacts as a transmission line (with +/- losses). This impacts the "how much sensitivity vs/frequency".
So, HF behavior of mains and interconnect cables may count. And it is maybe the reason why a "fantastic" cable used by somebody can sound "dull" on somebody's else equipment.
Yoghourt
P.S. not talking about HF, a mains cable gives a replica of *voltages*, not *power*. And electromagnetic compatibility is most of time a matter of *current* (so say my books, burr-brown, analog device, etc...).