I wasn't sure the Uncle Otis story would count as an answer to your question, as it seemed to me that Uncle Otis used his power in a controlled and purposeful (if deranged) way. Anyway, "Obstinate Uncle Otis" was first published in the July 19, 1941 issue of Argosy. Here is a rather similar story published five months earlier:
February 1941: "The Ultimate Egoist", a novelette by Theodore Sturgeon, originally published (under the name E. Hunter Waldo) in Unknown Fantasy Fiction, February 1941, available at the Internet Archive.
The narrator is a solipsist. One day on a walk with his girlfriend
"Let me put it this way," I spouted. "The world and the universe are strictly as I see them. I see no fallacy in the supposition that if I disbelieve in any given object, theory, or principle, it does not exist."
"You've never seen Siam, darling," said Judith. "Does that mean that Siam does not exist?" She was not disagreeing with me, but she knew how to keep me talking. That was all right because we enjoyed hearing me talk.
"Oh, Siam can exist if it wants," I said generously, "providing I have no reason to doubt its existence."
he is proven right:
"Your reasoning is typically feminine," I told her. "Spectacular but highly inaccurate. My point is this." I ignored her moans. "Since I am the creator of all this" — I made an inclusive gesture — "I can also be its destroyer. A case in point — we'll take that noble old spruce over there. I don't believe in it. It does not exist. It is but another figment of my imagination, but it is one without a rational explanation. I do not see it any more because it is not there. It could not be there. It's a physical and psychic impossibility. It — " At last I yielded to her persistent
yanking on my elbow.
"Woodie," she gasped. "It's gone! Th-that tree! It's . . . oh, Woodie! I'm scared! What happened?"
"Well, of course it's — " My lips flapped helplessly a couple of times. Then, "It's what?"
She pointed wordlessly at the new clearing in the copse.
"I dunno. I — " I wet my lips and tried again. "My God," I said very quietly."Oh, my God." I was shaking and stone-cold in the hot sun, and my throat was tight. Judith had bruised my arm with her nails; I felt it sharply when she let me go and stood back from me. It wasn't the disappearance of a thousand board feet of good spruce that bothered me particularly. After all, it wasn't my tree! But — oh, my God!
After a few more demonstrations of his power, he horrifies Judith by doing away with a person called Drip:
"Woodie, you’re impossible!"
"Could be. Could be. I've found a lot of things impossible in the last couple of days. They don't exist any more. Drip, for instance."
"Drip? What happened?"
I told her. She began putting on her hat.
"Wait," I said. "I haven’t finished my coffee."
"Do you realize what you’re telling me?" she whispered, leaning over the table. "That was murder, Woodie. You murdered that boy!"
After Judith leaves him, he gets drunk and loses control:
One drink and I felt better. Two, much better. Three, I was back where I started from. Four, I started getting dismal. Seven, I was definitely morbid. Great stuff. Far as I was concerned, the woes of the world were in a bottomless bottle, and it was my duty and desire to empty the bottle and buy another. Judith was gone, and without Judith there was no sun any more,. and nothing for it to shine on. Everything was
over, I said dramatically to myself; and, by God, I'd see that a good job was done of it. I staggered out and leaned against the door post, looking up the street.
"Wake up, Woodie," I quavered, "it's all over now. It's all done. There's
nothing left any more, anywhere, anywhere. A life is an improbable louse on a sterile sphere. A man is a monster and a woman is a wraith! I am not a man but a consciousness asleep, and now I wake! Now I wake!" I pushed away from the door post and began screaming, "Wake! Wake!"
Just how it happened I can't say. But things slipped and slid out of existence. There was no violence, and nothing fell. Everything went out of focus and left me alone in an element that was deep and thick and the essence of loneliness. What struck coldly into me was something I saw just before I — went. It was Judith; Judith running down the street toward me with her arms out, and a smile making it tough for the tears to run off her cheeks. She had come back after all, but the thing couldn't be stopped now. My dream was gone!
Woodie ends up like Uncle Otis in that other story:
"If all things in a universe were but peopling a dream, and if they could not exist when their existence was doubted," I thought, "then is it possible that I myself am a mere figment of my own imagi — "