This adapter allows you to use a 5.5 x 2.1mm DC power supply for a device that requires a 5.5 x 2.5mm power supply. Many of Allo's older audio boards feature the larger 2.5mm size, but their newer boards (2020) and Audio Power Supplies are all the more common 2.1mm size.
Input: 5.5 x 2.1mm DC female
Output: 5.5 x 2.5mm DC male