I looked around and was surprised nobody makes these, so I made them myself. You can buy this custom Korg Volca DC power cable from me here.

The Korg Volca range uses 9V power just like most fx pedals, but the input is centre positive (most pedals are centre negative) and the tip is a little yellow one used in lots of Japanese consumer equipment called the EIAJ-3. To connect your Volca to a standard pedalboard power supply, you need to buy an expensive adapter cable to get the right tip, and then another one to reverse the polarity.

OR! Just get one of these off me. I made a batch of ten to make it a bit more worthwhile. They are 60cm long, polarity reversing and work with all standard pedalboard power supplies. Drop me a message if you want a different length or a daisychain or something and I can probably quickly and easily knock you one up.