PP can be restored using several items. An Ether restores 10 PP for one move, a Max Ether fully restores PP for one move, an Elixir restores 10 PP for all of a Pokémon's moves, and a Max Elixir fully restores PP for all of a Pokémon's moves. Additionally, the Leppa Berry restores 10 PP for one move. In Generation II, Sacred Ash fully restores the PP of all Pokémon in the party.
The MysteryBerry (Japanese: ふしぎなきのみ Mystery Fruit) is a type of Berry exclusive to the Generation II games. It restores 5 PP to a Pokémon.
From Generation III onward, the MysteryBerry's spiritual successor, the Leppa Berry, appears instead.
Therefore, the items which restore PP are: Ether, Max Ether, Elixir, Max Elixir, Leppa Berry (or MysteryBerry in Gen II) and Sacred Ash restored PP in Gen II only.