I think what @DeepBlueMind is asking about is the power input on the Zynthian V5.1.
It is a fairly common “barrel” connector used on many guitar pedals. I believe it is 5.5x2.5mm but I’m not sure about that.
This power supply did work and fit:
https://www.amazon.com/gp/product/B0BDV15WYY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
and i did not need to use the adapter that came with it.
