Current shortage? (4)

I believe the answer is:

amps

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'current' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for amps that I've seen before include "'Units of electric current, in short (4)'" , "concert gear" , "Spam (anag)" , "Basic units of electric current" , "Units of electrical power" .)

I've seen this clue in the Evening Standard.

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