The One Spot comes in a few versions and while I don't need them anymore(I'm full battery powered to eliminate noise), I too have noticed a buzz on occasion.
I cannot remember how long my cords were at the time.
What Rev says is one possibility, but I've also noticed that running a powerful wall wart like the One Spot, into devices that don't need that much power, seems to cause the One Spot to buzz. It just has too much current. Some devices just can't handle it.
And yes, I've also noticed that some pedals sound different and/or better with more(or less) power than the factory suggests. It's not uncommon that premium distortion pedals(and pickups) can be run in 9v or 18v for example.
What you really seem to need is a battery system with enough juice to get the sound you seek.
This is the best way to avoid buzzes while providing a robust balanced power source with enough power to make your equipment shine.
The problem with battery power is, it tends to start out high and then decline.
The solution is to "regulate" the power for as much of the voltage drop as possible.
This is why I use the old version of boxking...the bk05 ; a regulated, rechargeable, 9,12 and 18v lithium battery pack.
They don't make them regulated anymore, and the bk05 is discontinued.
The only battery left that provides regulated 9v is on Amazon still, is made by Talent for $50 or so. However, it doesn't monitor how much power is
left on the one regulated outlet...the BK05 does. So it cuts out unexpectedly near the end. There might be new products available, I haven't checked lately.
But what you want is an old BK05 that still works or the answer to why a specific 30 foot cable acts weird.
Well, if I had a buck for every weird cable I've had, I could have bought twitter for cash.
And I mean, weird to the level that something SHOULD work...but just refuses to do so !
A lot of funny grounding issues can happen in old and new device mixes, and even in devices made in the same factory a few years apart.
And a lot of funny cable issues can happen very easily, sometimes without it ever being touched.
But if you want, here's another wild ass guess, the 30 footer doesn't buzz with the lower power wall wart because the power hasn't exceeded the cables limit to handle the buzz.
Use the higher power wall wart and it does !
Weird, yes.
Now this situation is making me hope I didn't toss any cables out due the high power One Spot but maybe I did !
Without a doubt, there is something odd about the One Spot, and for the money, since it claims to be regulated, I expected it to be as quiet as the Boss myself.
I was wrong. Now I don't use it unless it's powering a bunch of power hungry devices in a non-critical usage. That's what it was designed for.
Your setup doesn't need much power, and something is getting overwhelmed by excessive current. Maybe.
If you think that's a crazy idea, consider the difference in SOUND output/quality you notice with more current pushing your pedals.
Current flow isn't talked about much but my experience is that current "force" matters.
It's like water pressure in a water line. The One Spot has a massive current flow relative to the Boss.
I've run 12v going into a 12v unit at 1amp and it doesn't sound as strong and good as 9v going into a 12v unit at 5amps !
In this case, voltage isn't as important as current. Current matters !
And what it sounds like to me is, one or more of your devices is somewhat boosted by the higher current in the One Spot.
That's the beef that you want...and the Boss can't get you there.
I suppose you could try another "regulated" wall wart with more current than the Boss and less than the One Spot and see if that works better.
And if your Boss isn't 9V at 500ma(most common)... then that's something to try.
As for the 30 cable working in one configuration and not the other ?
Been there. Done that. Good luck.
