This power supply is ok in low-noise environments, if your instrument is properly shielded and if you're connected to ground through other equipment (like an amp).
However, this power supply will give you LOTS of noise (when not touching the strings) if:
-Your instrument is poorly shielded (or no shielded at all, like many cheaper instruments).
-You're not connected to ground (like if you're practicing with a headphones through a standalone preamp/pedal).
-There is noise inducing equipment close by (like stage lighting).
I never use cheap adapters like this one for any serious work, like gigs or recording sessions. I just wanted a cheap power supply for home practicing with my pocketPOD (which EATS batteries). I had used a Boss adapter in the past, with no issues whatsoever, but I needed the Boss adapter elsewhere. So I got this ultra-cheap Harley Benton adapter. Unfortunately it turned out to be useless. The noise became so loud that it was practically useless. The problem completely disappeared when I changed back to the Boss adapter (the one with the noise reducing coil on the cable), using the EXACT same setup.
To sum it up:
This power supply only works satisfactory with properly shielded instruments that are grounded through other equipment and used in controlled environments.
I would NEVER trust this power supply for gigs, where the noise environment can sometimes be unpredictable. It works ok under SOME conditions but a better quality Boss adapter (or a good quality power brick) will be a MUCH safer choice. To be fair the Boss adapter costs around 3 times as much but sometimes it's better to spend a little more and buy once, rather than filling up your home/studio/recording space with lots of noisy, low quality power adapters.
Of course, this adapter might be ok with YOUR setup, at least in SOME locations. But is it worth risking a ruined gig due to noise issues, just to save 20-30 Euros?
