What PSU did you use to determine that the current PSU is faulty?
Maker, Model, approximate age, etc.
The noise/ripple charts are all over the place with a quality review for a PSU with the same manufacturer. If the PSU you are using is old, capacitor aging could have greatly exacerbated the problems with the noise/ripple charts causing power delivery to be even more all over the place.
If the other PSU that was tested in this PC was equally bad, it would make sense that the exact same problem would continue.
If the test was done with an Antec, Corsair, Seasonic, XFX, or similar PSU with equal wattage, then I might think that it was something else.
Otherwise, this seems to be a PSU problem.