power hit

from Jargon File (4.4.4, 14 Aug 2003)

power hit
 n.

   A spike or drop-out in the electricity supplying your machine; a power
   {glitch}. These can cause crashes and even permanent damage to your
   machine(s).

from The Free On-line Dictionary of Computing (8 July 2008)

power hit

   (Or "power {glitch}") A sudden increase (spike) or decrease
   (drop-out) in the mains electricity supply.  These can cause
   crashes and even permanent damage to computers.  Computers and
   other electronic equipment should really include some kind of
   over-voltage protection in its mains input to prevent such
   damamge.

   [{Jargon File}]