I couldn't believe that this thing works!
I am a pedal and DIY freak... I build my own pedals, power suppliers, have a reasonable understanding of how electronics work.
I have some pedal that are VERY sensitive to power supply use; e.g. Germanium Fuzz pedals... and they do not like being powered by my Lithium Ion battery pack - give a terrible noise.
...I tried to build a filter myself; but didn't make a difference
This little gadget cleans things up 100% I really couldn't believe that it work! ...and at the price, very handy to have, just in case of a gig in a venue with an unstable power supply or other electrical interference.