PSU functions in one machine but not the other
PSU functions in one machine but not the other
Do you connect the Seasonic power adapter to the Corsair power supply, or have you updated all the power cables in your partner's computer after swapping the power supply?
Verify the cables to ensure you're not using any Seasonic cables with the Corsair PSU. The Corsair cables are marked "TYPE 4" on the connector that connects to the PSU. Because both Corsair PSUs function in your setup (which uses Corsair cables), I think there might be a Seasonic cable still present in the other system that's causing the issue. Confirm all cables are securely connected on both the PSU side and the component side. Make sure both the 18pin and 10pin connectors for the motherboard cable are plugged into the PSU side for the Corsair unit. If the problem persists after checking everything, consider removing components from the other system—CPU, RAM, motherboard—to test booting.