What can you do to be able to predict and prevent this? I suspect it was the psu but I’ll find out more tomorrow
I expect the average life expectancy of cheap OEM PSUs to be around 2-3 years. After that, you're on shaky ground.
You can likely extend the life of your electronics by keeping them constantly cool, and as dust/lint/pet hair free as possible (do yearly vacuum, use compressed air). This also greatly reduces the amount of combustibles in your electronics, meaning if something does overheat and die, there's nothing to burn.
As far as predicting it aside from it's lifespan, if you smell anything awkward, hear any funny noises, or notice any odd hardware behavior (blue screens, crashes, instability, etc) but especially "sudden shutdown and power-offs" then you know something is wrong. Just like if you suddenly get constant headaches, don't ignore it.
Might leave my home computers powered off from now on when I’m not using them.
…my brand new smoke detectors didn’t go off