From the doc
Add(CacheItem, CacheItemPolicy) : When overridden in a derived class, tries to insert a cache entry into the cache as a CacheItem instance, and adds details about how the entry should be evicted. [1]
-
Set(CacheItem, CacheItemPolicy) : When overridden in a derived class, inserts the cache entry into the cache as a CacheItem instance, specifying information about how the entry will be evicted. [2]
I see little difference in the wording (tries to) and signature (set is a sub, add returns a boolean), but I'm not sure which one I should use and if there is really something different between both.