I realized while writing this question that I have another issue with empowered objects. Specifically, it is the object using the stored powers, rather than the wearer/wielder/user. Can such an object "target" the user with personal or "self-only" powers? I intend to have a more powerful psionic NPC loan a PC a Psychometabolic item, but most of the powers it'll have access to are self-targeting and I realized I wasn't sure if the PC could even use them.
There might be outlier cases, but for the most part, the powers used by a vessel should affect the psionicist.
Empowered objects are explained to be intelligent weapons. From the Empower description: "The weapon has its own personality, however, and like all intelligent weapons, it will try to assert its independence at every opportunity."
As such, I would follow the rules for intelligent weapons. From the DMG: "Powers function only when the weapon is drawn and held and the possessor is concentrating on the desired effect. Most powers require that the character stop and concentrate for a full round."
Even though intelligent weapons are their own independent entities, they aren't capable of using their powers on their own. Given the involvement required of the player, I've never seen it ruled other than the wielder is also part of the casting.
2e didn't have a range of self. It just used a range of 0 and from the spell/power description, it was determined who was affected. For example, "Detect Good/Evil" one of the suggested powers for intelligent weapons: That's a spell with a range of 0 that is described as only affecting the caster.
Technically a DM could rule that the weapon is the one that detects who is good/evil and then communicates this to the player, but only 41% of intelligent weapons are even capable of speech. A full 34% are only able to communicate via "tingles and urges," so it seems unlikely to me that the authors intended such a game of telephone.