If there is anyone in this or any other universe who can defeat Lord Vishnu is Lord Shiva. In fact, there is a story in the Shiva Purana which states that Lord Shiva defeated Lord Vishnu and killed his sons. But generally, it is believed that they are equally powerful. Therefore, if there is a war between them, then the whole universe will be destroyed. One should understand that even an incarnation of Lord Vishnu or Lord Shiva is capable of destroying the whole world. When we talk about their powers, it is beyond our understanding. We can’t even imagine their powers; although it is possible to defeat incarnations of Lord Vishnu in some situations.
There are some stories in Hindu Puranas and some folklore that mention that Lord Vishnu was defeated.
Lord Shiva Kills the Sons of Lord Vishnu and Defeats Him:
This story is from the Shatarudra Samhita of Shiva Purana. After Samudra Manthan, Lord Vishnu took the form of Mohini and snatched nectar from demons. Gods drinking the nectar became immortal and killed most of the demons. From some stray drops of the nectar, some celestial nymphs were born who looked extremely beautiful. The remaining demons kidnapped them and went to the netherworld.
Lord Vishnu chased them to the netherworld. When he saw the beautiful damsels, he was enamored by their beauty. He began to indulge in sexual dalliance with those women of exquisite beauty. From these relationships, Lord Vishnu begot some sons from them who were brave and experts in many kinds of warfare. These sons of Lord Vishnu wrought great havoc in both heaven and earth.
Gods got worried because of this and approached Lord Brahma for a solution. Lord Brahma took them to Lord Shiva, and they requested Lord Shiva to stop Lord Vishnu’s sons from harassing the three worlds. Therefore, Lord Shiva took the form of a divine bull.
The bellowing bull entered the netherworld and shouted terribly. The cities and towns in the netherworld crumbled at this sound. Then the sons of Lord Vishnu, proud of their powers, attacked the bull. The bull kicked them with his hooves and tore them apart with his horns.
When Lord Vishnu came to know about the death of his sons, he became furious. He was deluded and could not recognize Lord Shiva in the form of the bull. He attacked the bull with arrows and missiles. The bull stood like a mountain and caught hold of the arrows and missiles. Then he leaped up suddenly and kicked Lord Vishnu. The bull then tore him with his horns.
After this onslaught, Lord Vishnu was freed from the delusion and recognized Lord Shiva. He apologized to him for his misbehavior and returned to Vaikuntha.
Charpatinath Defeats Lord Vishnu:
Navnath is a collective noun used to address nine great saints who spread Navnath Sampradaya, initiated by Lord Dattatreya, in the world. Navnath Bhaktisar is a devotional book that praises Navnath and depicts them as more powerful than the Hindu Trinity. In this book, there is a story that mentions that one of the Navnath once defeated Lord Vishnu.
Once Lord Indra insulted Narada Muni. Therefore, he wanted to avenge his insult. So, he took Charpatinath to heaven where they ate some fruits and plucked flowers from the garden. When guards in heaven came to know about this, they tried to arrest Charpatinath. Narada Muni immediately vanished from the place. Charpatinath defeated soldiers as they were no match for him.
One of the soldiers informed Indra about this. Therefore, Indra sent other gods to look into the matter. The gods attacked Charpatinath, but he defeated them as well.
Indra understood that he couldn’t defeat Charpatinath. Therefore, he went to Lord Shiva and asked for help. Lord Shiva and his ganas came to the scene, but they were defeated by Charpatinath.
When Lord Vishnu came to know about Lord Shiva’s defeat, he hurled his Sudarshana Chakra at the yogi, but the yogi threw some ash and immobilized it. Then the yogi used Vatakarshana Vidya against Lord Vishnu, which stopped his breathing. When Pippalayan came to know about this, he intervened and rescued Lord Vishnu and other gods.
https://www.hinduismfacts.org/navnath/navnath-bhaktisar/navnath-bhaktisar-adhyay-39/
Lord Vishnu Swallowed by Nigas:
Nigas was a demon who had obtained a boon from Lord Brahma that he would swallow anyone he wished once. He was a staunch devotee of Lord Shiva.
Per a story, when Lord Vishnu was in Yoga Nidra, Nigas swallowed him so that only Lord Shiva would remain.
Virabhadra Defeated Lord Vishnu:
According to the Shiva Purana, when Goddess Sati self-immolated, Lord Shiva sent Virabhadra to destroy Daksha’s yajna and kill Daksha. But Lord Vishnu had promised Daksha to protect him; therefore, he had a fight with Virabhadra where he lost deliberately, so that Virabhadra could kill Daksha.
Who Can Defeat Lord Vishnu?
I think the following are the situations where one can defeat Lord Vishnu:
1. If a person does penance and obtains a boon to defeat Lord Vishnu in his original form, then it is possible to defeat Lord Vishnu.
2. If Lord Vishnu Himself wants to be defeated, like in the Virabhadra story.
Conclusion:
Most of the stories that talk about the defeat of Lord Vishnu are from Shaivite literature. These stories are not 100% reliable because there was a conflict between Shaivites and Vaishnavites for a while in old times. Scholars believe that their devotees created the stories of Lord Shiva defeating Lord Vishnu and vice versa to prove the supremacy of their gods.
The saints who are unbiased believe that they both are equal in power and invincible.