Well, first off, according to this D&D Alumni article, the first appearance of psionics in D&D was in an appendix to the AD&D PHB, so no additional purchase was necessary.
Actually, that appendix (along with related material in the earlier MM and the later DMG) was a revision of the system presented in D&D Supplement III, Eldritch Wizardry, in 1976.
Several people have stood up to "take the blame" for those rules. From what I gather, the original version was a character class that someone (maybe Steve Marsh; my memory is fuzzy) had cooked up. There is probably a reference to the key source(s) of inspiration somewhere on the Internet! Someone else suggested breaking up the class and making the powers more widely applicable.
If you pick up Supplement III, you will find that only humans, and only certain classes (i.e., not monks or druids) have psychic potential. There are three lists of abilities: one for fighters and thieves, a second for magic-users, and a third for clerics. There is also a class-specific cost for each ability gained. Fighters lose followers, and a point of strength (thieves a point of dexterity) for every four abilities; magic-users lose spells; clerics lose spells and undead-turning power.
A number of longstanding elements in D&D were inspired by works that some folks might call "SF, not fantasy". The displacer beast is a well known example, its appearance based on that of the alien Coeurl in A.E. Van Vogt's "Black Destroyer" (who is, by contrast, quite intelligent and possessed of dexterous digits at the ends of his tentacles). The displacement illusion's being due to "molecular vibrations" is another reference to the story.
The deal with thieves hiding in shadows is rather a watered-down adaptation of Roger Zelazny's Jack of Shadows, a character whose planet is divided into constantly bright (scientific) and dark (magical) hemispheres.
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