> 1. Is the typical failure mode of 4-pin bridge rectifiers shorted or open?
> I don't do much with them.

Yes. ;)

> 2. Anyone want to tackle (just for fun) why it would have been the first
> component to go "pop" in this particular circuit when too much current was
> drawn from it?

It was the weakest component when the stressful event happened.

> 3. Anyone think "upgrading" either that MB352 or anything else in any
> fashion might make this particular power supply more "bullet-proof"?  It
> already doesn't have fused output terminals, and I can foresee a drill, a
> couple of panel-mount fuse holders, and a slight re-wiring job in its
> future.

Is it possible that the supply died when you switched it on with a
heavy load? If so, I'd look at limiting the inrush current, by putting
a low valued NTC in series with the primary. I'd probably replace the
electrolytics as well, given that they're at least 10 years old.

> I guess since I don't work with this stuff every day, I'm wondering if any
> sturdier "drop-in" replacements for the MB352 out there that might be worth
> stuffing in the thing, or would that generally be "a bad idea" for other
> reasons?  I'm going to be a little surprised if a component rated for 250V @
> 35A blew when the supply input AC line is fused at 5A.  Hmm...

In general, there's no problem with putting a bigger rectifier there.
But there's no point unless you have reason to think that it failed
because it's ratings were exceeded. Another possibility is that it
didn't meet its rated capacity, because it was damaged (e.g. during
manufacture) or because it was an outlier.

Other possibilities: Your transformer could be shorted. What are you
going to do then?
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