The ADD rules from Captain's Basic Set (G-rack ADDs are different, as stated earlier):
E5.71 Reloads
All ships equipped with ADD racks have two complete sets of reloads for the rack ...
Also:
E5.74 Reloading
One, two, three, or four anti-drones can be loaded on each ADD rack each turn, but only if the rack is not fired during that turn ...
Similarly:
FD2.421 (subsection under Reloads)
Up to two spaces of drones can be loaded on a given rack during a single turn, provided that the rack is not fired during the entire turn.
FD2.43 Stockpile
All ships are presumed to carry one complete set of reloads ...
Oh, and in case anyone cares, there are also ADD-30s, which are used by starbases and battle stations. Any approximation of this approaching 30 rounds must be from multiple ADD racks, which means the bases can fire more ADDs at once, but won't have them for as long, since they are using them simultaneously.
The point is, though SFC is not SFB, as it is now the shiplist is not standardized. At least FS is making an attempt to do that by using SFB as a guideline.