Power supplies sometimes do not age well. That's why I always preferred devices with a discrete PS. My oldest piece of electronics is my Heathkit digital clock. It's going to be 52 next year. Running pretty much continuously. With circuit traces a whole lot wider than they are now, older chips last virtually forever.
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This is a fine example of survivor bias which is why it's meaningless to reason about longevity of electronics without some data to back it up.
The Heathkit in question has a number of failure modes, which you've dodged or talked around. Firstly, the usual problem is the idiot who assembled it in the first place but that's an easy one to avoid (congratulations!). Secondly, Heathkit wasn't well known for picking the highest quality parts, particularly filter capacitors in the power supplies. Thirdly, the Beckman Panaplex displays they contain wear out reliably within 10-15 years with continuous use, symptomatic with emission dropping and/or segments crapping out. They also have a shelf life. On that basis, I'm also a little suspicious that this has been run continuously for 52 years. I've had numerous things pass through my hands and replaced numerous SP-352's in my time. I think the realistic life for one of those clocks, bar the outliers was more around the 5-8 year mark. The differentiating factor is it's actually quite easy to do component level repair on them (apart from the infernal ASIC that runs the show). I've got some electronic test gear which is 50-60 years old that works fine. It has been repaired but what is working now is probably 0.01% of the total items manufactured
With respect to somewhat more modern electronics, they have different failure modes but are generally a hell of a lot more reliable than anything we had historically but are more complicated. So the outcome is the roughly the same failure distribution. Really the statement with all electronics is worth considering:
Early failures - there will be a small number of outlying early failures ... <5 years
Mid-life failures - most failures happen here ... 5-8 years
Late failures - there are a small number of devices that survive this long ... >8 years
We love to talk about the very late failures though. They are merely an outlier on a pile of bodies a mile deep though.
What is worth bearing in mind is the expected warrantied lifespan of the device with the insurance (AppleCare). The insurance company wouldn't insure a device if they didn't think it was profitable. Hence why I buy new things and try and shift my devices after 3 years so the aggregate risk is pushed to someone else to deal with be that the manufacturer for early failures or the second owner for anything else.
