The rectangular power adaptor is the adaptor that is generally supplied with all our microphone systems. This adaptor has a male XLR to which you connect your standard microphone cable. The other socket is a mini-XLR to which you connect your microphone. This unit can use phantom power, if it is available from your mixer/amplifier, there is, however, and option to fit a battery when phantom power is not available. There is a slide switch on the side which provides a bass roll off. The same slide switch will switch off the power apdator when using battery power but will not switch off when on pahntom power. This version has a rotary violume control allowing the instrument volume to be adjusted without having to go to your mixer/amplifier.