I'm not surprised the surge protector worked, as it was a good one, Pete. What surprises me is that it still allowed power through
after the hit, i.e. when you switched it all back on. The principle they work on is that the surge protector is a big capacitor. It takes the hit and at least one of the two capacitor plates buckles. In the case you describe, one has probably melted and the material which formed the two plates may be touching.
So now you've seen what it can do, replace it quickly. It won't survive a second, even a much smaller hit. And you've seen how much money it can save, how many huge problems it can prevent. And like you say, pay for a named, guaranteed one. It is one item simply not worth compromising on.
Which reminds me. I'm flogging expensive electronics. Time I got a stock of surge protectors to go with them.
And thanks for reminding us of that very important omission.