SMC on Macbook with non-removable battery: (Google for different instructions if you do have a removable battery)
combo updates can be helpful for troubleshooting a failed Mac OS X update, and running through one can often remedy a broken or borked update attempt.
What is a Combo Update?
Essentially Combo Updaters allow for updating a Mac from a prior version of OS X within the same major release, without necessitating the Mac being on the immediately preceding version point release. In other words, it’s a combined update, including all necessary components from prior point releases