According to the documentation,
If the feature class is enabled to store CAD entities, a side table is created for the feature class to store CAD data, such as curves. All feature classes created through ArcGIS for Desktop are set to store CAD entities. If data is imported or registered with ArcSDE using ArcSDE administration commands, you specify whether or not CAD data can be stored in the resultant feature class. The feature class diagram also shows a CAD table, SDE_geometry42. The 42 in the table name refers to the feature class's layer_id from the SDE_layers table.
Therefore, your 'SDE_geometry276' table references the CAD objects associated with layer 276. If layer 276 no longer exists, you can drop this table.
However, I urge you to review your geodatabase for other corruptions, and to review your procedures to determine how orphaned table(s) became orphaned.