Robert Myers wrote:
Last summer I bought a box from a very big OEM at a good price.

The box would not boot on delivery because the RAM had been installed
incorrectly, so it's clear that, if the box was tested, it was tested
before the RAM was installed, and now I'm wondering at what stage of
assembly the boxes are supposedly tested (not at all after assembly?).

The stage where the end user tries to boot the box, at least from the vendor you
used.

I increased the memory by 50%, reinstalled the incorrectly installed
memory, and added a second HDD, and the machine did boot.

I haven't used the machine much, and, in particular, I haven't used the
video much, but this summer I started encountering video problems while
trying to upgrade Fedora.

Since I had an extra video card available, I tried changing video card.
My replacement video card drew too much power and the machine would not
even boot. The easy conclusion was that the power supply was either
malfunctioning or marginal to begin with.

That's a fair guess, many are sized to the need as sold. That's not an unfair
practice, just one which should be more obvious before it bites you.

The computer store is a fair drive, so I bought both a replacement power
supply and a very low end video card. I don't like replacing power
supplies, so I tried the video card. Works like magic. I'll replace
the power supply if I get around to it. I mostly run the box remotely
and I don't need fancy video. As far as warranties are concerned, I
can't imagine what circumstances would make a warranty repair worth my
time, so I don't worry about it.

Unless you have some reason to use a brick and mortar store, places like newegg
and tigerdirect are good sources for parts.

Maybe when you pay for installed upgrades, you pay for an upgraded power
supply. Since the memory was added to this box with no further testing,
it's easy to imagine that boxes might be shipped with upgrades such that
the power supply is often marginal or inadequate.

Anybody have any insight?

Except for gamer machines, vendors expect the cover to stay on. The bad memory
install would have gotten a complaint from me, I doubt anyone ships without a
smoke test, at least not anyone remotely reputable. I bet someone saved a bit of
time by not doing it as s/he should.