Shocks almost guaranteed power increases (9)
I believe the answer is:
surprises
'shocks' is the definition.
(I've seen this before)
'almost guaranteed power increases' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'guaranteed' becomes 'sure' (I've seen this in another clue).
'power' becomes 'p' (symbol in physics).
'increases' becomes 'rises' (rising is a kind of increasing).
'sure' with its last letter taken away is 'sur'.
'sur'+'p'+'rises'='SURPRISES'
(Other definitions for surprises that I've seen before include "Astonishes" , "Takes unawares" , "unexpected things of life" , "bowls over" , "Sudden, unexpected events" .)