This is an old AC adapter from BOSS, apparently for the BX-8 and BX-16 mixers. The connector on the equipment side is a special mini 3-pin plug. (This was included with a different piece of used equipment I bought for some reason) I don't have a BOSS mixer here, so I can't confirm if it works, but I'll sell it to someone who needs it. - Brand: BOSS - Model: ACE-100 - Input Voltage: AC100V 50-60Hz 18VA - Output Voltage: DC 21.5V 300mA - Made in Japan Thank you for looking.