Andrew had a high-end system. Tannin built it a year or two ago, and, possibly because he was having an unusually good day, managed not to stuff it up. It was approximately as follows: Athlon XP 1800 (old style), 512MB, Leadtek 256MB Gforce 4ti, Sound Blaster Live (or possibly an Autistic, I forget), CD burner, DVD. Over the nest year or two, we added a second hard drive, swapped the CD burner for a DVD burner, and Andrew fitted two more sound cards. (Yes, three sound cards. He is pretty serious about his sound, young Andrew is. Does a lot of recording stuff.)
It was powered by a good quality 300 - I forget the brand, but a specialist low-noise one - it worked fine. I think we wanted a bit bigger than 300 in the first place, but you couldn't get 350s or 400s in low noise back then, and the low-noise was important to him.)
It may or may not have started misbehaving later on in life - I'm not sure about that, as it wound up with a phenomenal amount of software loaded, and any issues may have been masked by that. Being Win 2000 based, it put up with that surprisingly well. A Win 98 machine with that amount loaded would never have booted, never mind about useful work.)
It came in for upgrade a month or so ago. The plan was to slip in a new main board with USB 2.0 and an XP 2800, plus up the RAM to 1GB. If possible, we were to retain the Windows installation.
I bolted all the nice new bits in and immediately struck problems. Mostly it wouldn't even complete the boot process, though in safe mode it would usually stagger along OK. Despite some video corruption, power was my first thought, so I swapped in a Bliss 300 - a power supply that until then had practically never been proved wanting. A little better, maybe, but still clearly sick. Not the power supply, it seemed. I tried another one though, just in case. It occured to me to try a bigger PSU again, but the only 400s I had on paw were middling-cheap ones. I tried an Omni but, as expected, without making a noticable difference.
So then I started fault-finding. Several times I thought I had an answer but the results were inconsitent. It was only when I swapped the video card that things started to come clear. As soon as I flexed the 256MB ti and popped in a Gforce 4MX, it improved a good deal. We fiddled about and got it so that it seemed to run, meanwhile ordering a Leadtek Gforce FX5700. When that arrived, it immediately presented the same minor video corruption problems as the ti had done. Both cards worked fine in other machines.
Sure enough, when I bolted in the lavisly expensive 420 Watt PSU I'd ordered earlier, the system finally sat up and kicked arse. It now works perfectly.
Now we handle a good many systems, and that is at this stage the only one we have met anytime recently that we can definately state needs more than a good quality 300. There is a second one that the jury is still out on, but I think that might be the same thing. He (the second customer) doesn't have the outlandish sound gear that Andrew has, but he does a nice line in multiple hard drives and works his system hard. I'll know in a week or two.