pedal PSU buzz...again

Hey all,

I have a few pedals and small transistor amps which all work perfectly with an old generic 9V 500ma PSU that I have.
I only have the one PSU for all devices, though, and i'd like to have a spare.

I ordered up a few 'noise free' psus of equivalent spec and found that they all buzz like crazy.

It's that 'bad ground' type of buzz that goes or way or calms down quite a lot when you touch the guitar strings. Moreso if you're actually holding the guitar close to your body and touch the strings.

I have several of these amps, pedals, and several guitars - It's conclusively narrowed down to the new PSU but my question is why?
There's literally zero hum or buzz on my old generic adapter and the big sell on these new Psus is the 'fact' that they're noise free.
Can anyone tell me what the difference is likely to be?

I've no doubt I'll be able to get a refund on these but I've no idea what to buy in replacement.

Many thanks in advance.
 
Well apparently the seller's 'noise free' power supplies are actually switched mode supplies which just so happen to be silent with one particular model of zoom effects pedal. :facepalm:
He says they're specifically for that model of zoom pedal, although the label may as well say 'cheap generic chinese crap' on it. :p

He kindly agreed to exchange for linear supplies which are working just fine so everybody is happy. :)
 
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