I want to make sure this never happens again, so buy a decent surge protector ($20 or so?), unplug my stuff from the outlet when I'm not using it, and that's basically all I can do right?
Power off does not cause damage to any electronics. You probably had the most common reason for supply failure - a manufacturing defect.
For example, another had your symptoms. Used speculation to make the same conclusion. I traced their failure to a pullup resistor on a voltage regulator. That resistor had only one function. To boot the regulator during power on. That resistor probably failed months ago during normal operation. But the failure was only noticed months later when it failed to do its only job - during power up.
They had a manufacturing defect. Yours is most likely same.
Meanwhile, that protector claims to protect from transients that are typically not destructive. Spend $25 or $100. Then have a circuit similar to what sells in Wal-Mart for only $7. Those 'adjacent to computer' protectors are profit centers. Read its specification numbers. It does not even claim to protect from the typically destructive surge.
Another completely different device is also called a surge protector. That other surge protector is the only viable solution. And it costs tens of times less money. 'Whole house' protectors come from manufacturers with much better reputations including Siemens, Leviton, Cutler-Hammer, Square D, Keison, ABB, Intermatic, and General Electric. One means everything is protected even from direct lightning strikes.
Either buy a protector that is a profit center. Or buy one that is proven by over 100 years of science and experience. You are asking about protection from something that occurs maybe once every seven years. That is completely different from what typically causes most failures - a manufacturing defect.
One final point. Good luck finding anyone who can repair a supply. I can. But then I have been doing this stuff for decades. Repair only to learn about what caused a failure. Do it only to avert future failures. Most computer techs do not even know how electricity works. Will only replace parts until something works.
Others have recommended not learning why a failure happened. Just replace the supply.
