Expense of electrical supply (6)

I believe the answer is:

charge

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'expense' is the definition.
(I know that charge is a type of expense)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for charge that I've seen before include "Entrust (with a task)" , "running cost" , "Rush to exact payment?" , "Formal accusation" , "Price for a service" .)

I've seen this clue in The Globe and Mail and The Irish Independent.

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