When they're not powerful enough, you don't need a bigger compatible one, you just need more on the 12V line. Just get any old PSU and use it in addition.

Works only with PSUs, that don't require significant load on 5V to keep the 12V line at the right voltage. Some won't even turn on without something @5V.

Those are really rubbish. Any decent supply has no such limitation. And in fact the PSUs I use for GPUs only have a 12V output! HP blade server supplies, £12 for 2.6kW at 97% efficiency, can't get much cheaper than that. If you want to use a supply you found in the local skip, simply place a load on 5V, a lightbulb for example, or something useful like some cooling fans. Actually, to require 5V current to make 12V work is utterly ridiculous. Why would one rail care what the other is doing? Must be some weird botched together circuit in there. A proper power supply generates 12V, then creates lower voltages from that. Even if the 5V was generated from scratch from the 240V, why would it affect the 12V part? I've got some of the cheapest PSUs available for powering the MB/CPUs. CIT supplies. Where it's pronounced with a soft C. They work, but 12V is rarely 12V. Somewhere between 11.3 and 11.9 (yes, even with 5V loaded). The MB/CPUs are happy enough on them, but old GPUs want more volts, I like to run them at the max 12.6V, keeps the tired ones awake. So those CIT supplies, they start up and run just fine with only a 12V load. I've got one running the window fans in the garage to stop the room overheating in summer, and one powering extra stuff - fans for the xeon CPUs where the weird Dell MB has non standard connectors, instead of bothering to hack into the 12V line from their own supplies, I just use this one, it also powers the SSDs as for some reason there's no molex or SSD power connectors on those supplies, maybe I'm missing a riser board, and a booster fan for the laptop which gets far too hot with the pitiful one inside it.

By the way metal shelving is a bad idea, you're asking for shorts. I use wood.

I understand why you are worried about shorts, but in general, as computer cases are made of metal, there's nothing wrong about putting them on metal shelves. Server racks aren't made of wood either and nobody worries about shorts there eiter.

But we're not using professional servers in cases. I for example simply place the GPUs flat on the shelf. If it was metal, all the solder joints on the back would be connected together. I can't fit 6 GPUS into the desktop case. They sit next to it.

[cpuquote]

My HP and Dell pc's are model Z600 and T5500

Probably you even can't use anything else than the original PSUs, the HP mainboard seems to have non-standard 18-pin connector according to the pictures I see on Google and Dell is known to use own wiring on standard ATX connectors, so you'll burn the mainboard and/or the PSU if you use anyhing else then the original PSU.

I'd never buy a desktop computer not build out of standard parts, when anything fails, it's just scrap as replacement parts are usually very expensive for such systems or not available at all once they run out of support. Well, I'd never buy a prebuild destop computer, but that's another thing.[/quote]

I have 6 of these pc's and they each have dual Intel Xeon quad core cpu's that think they are 8 core cpu's, so 16 cpu cores in each pc AND I got them for $250US shipped to my door only needing a harddrive and a gpu to run. They all came with 16gb of ram as well which I have upgraded to the pc max of 32gb except 1 pc that has 2 bad memory slots in it so it only has 24gb of ram in it. They crunch everything I've thrown at it so far except LHC and LHCdev but that's probably something in the software, Linux or Windows, that's not been updated. Some have Windows on them while others are running Linux and they are 96 great Boinc crunching cores. They are off business lease pc's so I got them at a huge discount.

I have used an adapter in regular Dell pc's before to upgrade the psu and that has worked great, they make 24pin to 8 pin Dell mb connectors. The only thing is they have to stay in the original case because of the way the power on/off, the sound and the restart buttons are wired into the mb they use a plug not individual wires and I've never found an adapter for that and I'm not running a bump switch to start the pc. The older pc cases have very poor airflow and no top fans at all so modern day gpu's don't do well in them.

I have 6 of these pc's and they each have dual Intel Xeon quad core cpu's that think they are 8 core cpu's

You mean they're 4 cores / 8 threads?

so 16 cpu cores in each pc AND I got them for $250US shipped to my door only needing a harddrive and a gpu to run.

You don't need a GPU to run a computer.

They all came with 16gb of ram as well which I have upgraded to the pc max of 32gb except 1 pc that has 2 bad memory slots in it so it only has 24gb of ram in it. They crunch everything I've thrown at it so far except LHC and LHCdev but that's probably something in the software, Linux or Windows, that's not been updated.

LHC should be fine, I've got it running on an old 4 core with 6GB of DDR2 RAM! Theory is easiest to run, older CPUs crash CMS, and Atlas needs a lot of RAM. The only requirement is Virtualbox. And LHC will run with Virtualbox 5, 6, or 7. I use 5 because that works best with Cosmology.

I have used an adapter in regular Dell pc's before to upgrade the psu and that has worked great, they make 24pin to 8 pin Dell mb connectors. The only thing is they have to stay in the original case because of the way the power on/off, the sound and the restart buttons are wired into the mb they use a plug not individual wires and I've never found an adapter for that and I'm not running a bump switch to start the pc.

Why not just use a big normal tower case, and take the switches off the Dell case? Just fix them to the new case in some way, use one of the 3.5 or 5 1/4" bay covers to glue or screw them to.

The older pc cases have very poor airflow and no top fans at all so modern day gpu's don't do well in them.

I prefer to keep my GPUs outside the cases. Or leave the side off the case.