I have a Marshall 2203 full stack in right now that gets played with the gain on 8 and turned up to deafening levels. It's highly sensitive to any kind of noise and has three pedals running daisy-chained off a cheap Chinese SMPS supply. It's a noisy setup and my gut feeling was that the supply wasn't up to it and was bound to be causing additional noise. So I subbed in a brand-new One-Spot Pro CS7 and connected each pedal individually to a single isolated output with short leads and no daisy chain.
Zero difference. No detectable change in hum or anything else. There's a slight bleed from a Chorus pedal oscillator when in bypass mode that's there with both supplies. I also tried my bench supply with the same results.
The lesson from this is that something that may be perceived as a problem in reality may not be an issue at all. You (and I) may be wanting to fix something that is just fine like it is.