In the past, I had a few pedals which needed a 3.5mm jack to power them from a PSU (ProCo Rat, EHX Small Stone/Small Clone).
I simply modified a few of the leads with a 3.5mm jack I bought from the local music shop, figured out the positive & negatives, then soldered the leads to the jacks. Lasted for years with no problems. Sold the pedals and included the leads.