That is simply not true, I documented it like 10+ years ago that PSU's were failing in STEs. I even documented why on my site. Bad caps. I've had like 200 PSU's through my workshop, none of which will power a STE with 4MB RAM (but mostly work OK with 512K) . SR98's are ( in my book) the ones which typically fail first. Re-cap them, they work better than new. Some others like the DVEs tend to live a lot longer, though I have not seen more than about 20, so not a huge sample range to try.
Old caps indeed can go bad. But also I've worked for a company repairing volumes of switchmodes. Was lucky to get 3-6months out of caps in the things.
One of the big gaming companies purchased a large number of ABIT motherboards, and at the time I always used to use them as liked their products. I remember ABIT refusing to replace all the motherboards under warranty as all the caps kept blowing up in under 3 months. I'm talking like millions of motherboards not just not few.
Similar with several large manufacturers of power supplies used to deal with. The amount of capacitors we had to change was unbelievable. They would hardly ever get past 6 months use. Of course a lot of it was bad circuit design, bad implementation etc. ST PSU's have done remarkably well compared to all the more modern power supplies which I was seeing my old job.
My point being that simply age of the capacitor is only part of the story. How it is used and of course quality of components is also a factor. It can actually get pretty complicated.