Yeap Philip in general this is the main concept. A real PC-system needs to be installed in a damn silent environment to get readings below 30dBA and also even the slightest noise from the system will alter the readings, and we are interested only in the noise of the PSU.
As for programmable PSU I plan to test the whole fan operational area and not only the values I measured through my tests. Although in my auto crossload tests I run thousand of tests and I have to replicate all of them. For this a program is needed that will control both the db meter and the PSU, gather the data and save it. Afterwards this data will be analyzed by another program that I wrote and the result will be the graph shown at post #1. It needs lots of work to be done but I am sure that the result will definitely worth it.