I'm still doubtful a lab power supply is used. It just doesn't make any sense. A lab 'bench' power supply provides DC, not AC. Also, these components are consumer products meant to operate off of standard household power. If you want to measure and test them, wouldn't you want to know the performance given wall power?
No, I don’t think so.
One would want just the noise and distortion from only the unit.
But many would also want to know how the unit operates with dodgy power.
Since we do not know what different cities, countries, and individual houses power looks like, then the easiest is just use pure sine wave power.