Voltage-changing device (11)
I believe the answer is:
transformer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">voltage-changing device</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for transformer that I've seen before include "Electrical voltage changer" , "Voltage-changing device" , "Device for changing voltage" , "piece of electrical equipment" , "Electrical device used to change voltage" .)