As part of the recent April 2016 PSU Patch release for Enterprise Manager (EM), a list of recommended patches has been compiled for EM 12c. This list contains recommended patches for the EM infrastructure including the OMS, WLS, Plugins, Repository and Agent. These patches are also included in the Exadata Quarterly Full Stack Download patch.
For more details and to review these EM recommended patches for Exadata monitoring, refer to My Oracle Support Note titled Patch Requirements for Setting up Monitoring and Administration for Exadata [1323298.1]. This note was to provide a list of the recommended patches for monitoring an Exadata Machine but can be applicable for any EM environment. Just keep in mind that your EM environment may require other agent plugin bundle patches depending on what target types are managed in your EM environment.
Also, the information in the note contains not only a recommended list of patches for both EM versions 18.104.22.168 and 22.214.171.124 but also provides a link to a My Oracle Support Note that provides the steps for applying these patches. This note is titled Applying Enterprise Manager 12c Recommended Patches [1664074.1]. The patch apply process in this note provides maximum availability for the EM environment by structuring the patch apply steps so that the primary OMS server is up as long as possible.