The Templo guys (guy?) advise linear (and a dedicated psu). I had an 18v switching one to hand and voltage leaked into the audio as soon as I turned the tone up. BUT the one I had was center-positive with an polarity reverser extension, so frustratingly I don't know if it was the reverser or the switching nature of the psu that caused the issue.
People seem to like the Dunlop one (is it the only option) but I also gather that one can be squealy under the wrong conditions, and this pedal seems particularly sensitive.
If a linear 18v centre neg UK psu exists I'd happy to pay a few quid more rather than start buying more stuff to return.