Question Which size cable plug fits into the external power supply jack for the BLD / DPE / SCF / SPE / XII pedals The manual gives the voltage requirements and such, but does not address this issue. it appeared to be a 3.5 mm mini plug, but that doesn't seem to fit perfectly.

Please have a look on the website of Cliff Components. Please type CL1062 or CL1066 in their search box on the upper right side. These are the mating plugs for the sockets we use(d). (US contact details are shown on the right side of the site). These plugs are also 3.5mm types, but as you can see, by clicking the pictures of these plugs, the tip has a slightly different shape compared to i.e. the FT6300, which now is a more common 3.5mm type (you can use their search engine to get a picture of this plug).