What makes the decisions.
A computer powers on or off only when a power controller makes that decision. Even the CPU cannot execute a single instruction until the power controller permits it.
One of the many power controller functions is a safety lockout. Once triggered, the only way to reset the safety lockout is to disconnect the plug from AC mains. You apparently reset the safety lockout. Few even know that function exists.
Neither a UPS nor power strip is relevant. A UPS has only one function. To provide temporary and 'dirty' power during a blackout. So that unsaved data can be saved.
Meanwhile your computer comes from a more responsible manufacturer. Therefore it has comprehensive hardware diagnostics that can boot before the BIOS tries to load Windows. To confirm hardware is working properly. Best time to execute those diagnostics is long before any problem exists. So that you know how to execute them. And know what a good computer does.