The most common and most likely answer to this crossword clue is the 5 plus 5 letter word TIDAL RIVER
I've seen this crossword clue in The Guardian
T
I
D
A
L
R
I
V
E
R
Buddy explains!
The straight part
We know that "Where to find alternating current" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case where to find alternating current = tidal river.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.