I use one similar in the back of my Ampeg SVP1600 power amp. Except there is a male prong end on the combo plug and the female on the other end. Then the pigtail end is a female connection.
I place my preamps 12v adapter into the female combo after connecting to the power amp outlet. Then connect my power cable to the Eventide PowerMax that is powering all the pedals to the pigtail with an extension.
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The main power cable from the amp connects to a 25' extension cord that I run to the nearest power conditioner on a stage.
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Works like a charm!