Because I was in a rush to make my previous post I skipped over your question, so I want to back up a little.
"...does Windows do anything special when using 4GB that would make it run like shit if 2GB is taken away? It's running so slow and thrashing the HDD constantly".
Not particularly. Obviously, it depends on what's loading at startup. If what's loaded consumes more than 2GB, the overflow is pushed out to the swapfile/pagefile on the HDD, which would account for all the drive thrashing.
To get a cursory view of what's running (and how much memory is consumed by each item) you can use the Task Manager and/or Resource Monitor. For how to interpret various indicators see Measuring memory usage in Windows 7. For a more granular view you can download the free Process Explorer from MS's SysInternals division. It's like Task Manager on steroids, and will let you identify hidden processes nested by either SvcHost.exe or RunDll32.exe.
You can use the MSconfig utility to prevent unneeded/unused programs from loading at startup. (AutoRuns is the free steroids version of MSconfig). You can do the same for Windows Services; have a look at the Black Viper's site. Be sure to see his Win7 SP1 Service Configurations page. By disabling unneeded/unused services and programs you can significantly shave your memory footprint.
You may also care to see RAM, Virtual Memory, Pagefile and all that stuff, which should give you a better idea of their relationship to each other. Various versions had been previously published by MS as KB2267427 and KB555223, both of which have been removed.
Moving on to your immediate problem, unless you know for sure that the "lovely fop sound" you heard came from the PSU, I would be cautious. If you can, try substituting another known-good supply before buying a new one. You want to make sure the supply you had been using didn't take anything else with it for the ride over the cliff.
I'm assuming you've run your requirements by a few of those PSU Calculators? (Thermaltake has their own calculator).
The PSU Stickies at the Overclockers forum are also a good resource.
The 575 Watt Thermaltake Toughpower XT (P/N TPX-575M) has good specs all around. It's a similar design to the Corsair TX650, so you may want to look at a few PSUs from Corsair.
I also took a look at the 550 Watt OCZ Fatal1ty Series.
Personally, I would go with the Thermaltake. Not only for the better warranty (which is a good measure of the vendor's confidence level and expected MTTF/MTBF), and the solid dielectric capacitors. But, according to Newegg, it's also EPS12V (v2.91) compliant. Because EPS12V supplies are often employed for high-reliability server use they use a failsafe design that minimizes the likelihood of follow-on (domino effect) damage of anything connected to them.
From my perspective, unless it's a throwaway box, the PSU is not the place to pinch pennies.
Something else to consider is what I call the "dust bunny margin". What many used to do is deliberately oversize the supply to obtain additional thermal margin before having to clean out the dust bunnies. Unfortunately, with many new, high-efficiency models (compared to older, lower wattage units) there is often no increase in heatsink size or fan CFM when going to a higher wattage model. The result being there's no increase in dust bunny margin before overheating occurs. So you wind up having to clean it out with greater frequency.
It's worth noting that excess heat can significantly reduce the life of most passive components. For instance, electrolytic capacitors are typically rated for use at a nominal temperature of 25°C. For every 10°C above that temperature the rated MTTF (i.e., expected life) will go down by half. So if a part is rated for 50K hours at 25°C, it's only going to get 25K hours at 35°C. Just something to keep in mind when premature failures are encountered.
Unfortunately I don't have a spare PSU with a P8 or any PCI-E connectors. I've had two previous PSUs blow up, one took out the motherboard with it and the other caused no collateral damage. The PSU calculator suggests 412W with some capacitor aging so shouldn't be overloading it.
Actually I had trouble starting the old computer recently with this PSU so wouldn't be surprised if it had died..
I do usually do a bit of optimisation to reduce memory usage as much as I can which I didn't do with the 4GB installed as it was running super smooth anyway so could just be it's using more memory than usual and using the swap file lots.
I've taken the PSU out and opened it up (without electrocuting myself this time (although that was about 10 years ago)) and it looks like the PSU suffered the same.fate as the old motherboard, leaky capacitors. Probably why it was playing up.now and again. Not sure what went pop though, nothing obvious.
So need to send the RAM back (should Scan pay the postage?) and order a new PSU and hopefully I will have a stable computer at last.
"Not sure what went pop though, nothing obvious".
Most electrolytic caps have a safety vent on their bottom. You will hear it blow, but there will usually be no visible signs on the PCB top side, other than possibly some expulsed electrolyte around the cap's sides.
"I was quite surprised how much dust was inside the PSU which certainly wouldn't have helped it's lifespan".
Hence, my mentioning the "dust bunny margin".
"And unlike the inside of the computer it's not something that can be removed easily with the little warranty stickers they put on the screws".
Which is why I either ignore those stickers (as more than a year is really too long to wait) or put a sticky note, having the warranty expiry date on the case's outside, reminding me to do a cleaning as soon as possible thereafter.
It also helps if you have a case that has a removable filter on the air-intake, like some Lian-Li models.
The vent is supposed to be the scored mark on the top and the plug at the bottom. Not sure how that works on the bigger ones though because they don't have the ridges on the top, or at least the ones in my PSU. There are some pictures on wiki showing exploded caps where the whole casing has come off and showing the insides.
Looks like I have 5 of them dead. 2 bulging, 2 leaking a little out the top and 1 where the bottom plug has been forced out. Definitely dead, but I felt a bit odd pulling the caps off it.
"The vent is supposed to be the scored mark on the top and the plug at the bottom".
Most older designs used the scored topside as a backup. A few vendors used it as the sole venting means. But most just have the bottomside vent plug.
Between 2001 and 2003 the market was flooded with bad caps. The problem had serious impact on both MoBo and PSU vendors, among others. A lot of products containing bad or marginal caps are still out there.
At the time, it was written up in the Electrical Engineering Times and other trade rags. Rather than go digging for those old, dry technical articles, have a look at PCmag's Hushed-Up Disaster Dept.
To better help identify bad caps, be they on the MoBo or in a PSU, see the following:
• Bad System Board Capacitors!
• How to identify bad capacitors
The above have plenty of good close-up photos.
"Looks like I have 5 of them dead. 2 bulging, 2 leaking a little out the top and 1 where the bottom plug has been forced out".
Sounds as though your PSU was long overdue for replacement.
I read the vent bit on Wiki's Capacitor Plague page. Apparently bad caps been seen since 1999 and still used in some products made this year. Something to do with the formula of the dielectric which causes a build up of hydrogen before it pops. I'm sure that's what I heard happening.
The PSU was only 2 so I'm surprised it was so bad. I hope it hasn't damaged any of my new components. I guess I'll find out when I finally get my new PSU and RAM back.
"I read the vent bit on Wiki's Capacitor Plague page".
I hadn't heard it referred to as "Capacitor Plague" (at least not in the engineering trade press) but that phrase certainly turns up plenty of hits, including the Wikipedia page you mention.
"Something to do with the formula of the dielectric which causes a build up of hydrogen before it pops".
Over time, all electrolytic caps out-gas some hydrogen. It's a matter of degree. (i.e., how much and how fast).
"The PSU was only 2 so I'm surprised it was so bad".
It could also have been that "dust bunny" thing (excess heat build-up) or in combination with marginal or bad caps.
According to wiki again, the capacitors produce H instead of the electrolyte evaporating. I don't think I've ever had PSUs die so quickly, both Hiper ones, 2 within 5 years. Even cheap/case bundled PSUs I've seen longer than that.
The last one was a 580W but only did 360W on the 12V, not good according to a review. And THG did a PSU stress test in 2006 and the model I have failed: " the results were in violation of the specification." I think it may not be a very good one.
"According to wiki again, the capacitors produce H instead of the electrolyte evaporating".
Sorry to be somewhat pedantic, but parts of the article are poorly worded. As previously stated, all electrolytic capacitors produce some hydrogen gas. What they should have said is the improperly made ones produce it to excess.
While I like Wikipedia, and frequently cite it, just bear in mind that it does frequently contain inaccuracies. One of the early warning signs the author was sloppy is the inclusion of one or more "citation needed", "original research", or other similar notices. For a general overview it's fine. But if you're writing a paper for university or other important work, don't rely on Wikipedia. But do look at the references and the "last modified" date, as there is often newer research.
In this case, reference #1 (2004_Electrolyte_Hillman-Helmold.pdf) tells the story. See PDF page-1 (actual page 122), second column, the last four paragraphs, with the formula sandwiched between the second and third paragraph. If you're not interested in the details, just take note in the last of those four paragraphs of the words "excessive hydrogen".
"I don't think I've ever had PSUs die so quickly, both Hiper ones, 2 within 5 years. Even cheap/case bundled PSUs I've seen longer than that".
Thanks for the postmortem. Note to self: Never, ever, use a PSU from Hiper! Replace on sighting (or advise replacement) unless rightful owner owes me money! :D
I didn't mean to question your knowledge, everything I learned about the things was from that article (although I should know a bit about how they work from the university course I started) so it's nice to be corrected. So will all capacitors eventually pop/vent?
I did buy the Hipster PSU (exppecting it to be good quality) just before I moved into my house so it could be that my house has vast quantities of dust which are not friendly for PSUs.
I want my.computer back so I can play Skyrim :(
"I didn't mean to question your knowledge..."
I didn't even take it in that context. So no need for clarification. But, as you can probably tell, I've been at this awhile. I just didn't want you to assume the Wikipedia article should be taken at face value, no questions asked. (And in all fairness, I've periodically had my own share of brainfarts ;-)
"So will all capacitors eventually pop/vent?"
That should be "all [electrolytic] capacitors...". No, not necessarily. But at some point they will cease to function as the electrolyte becomes inert. Think of an electrolytic capacitor as a specialized battery. Their respective chemistries are not dissimilar.
For a non-defective part the main instigator of excessive out-gassing is heat. It doesn't much matter if it's externally or internally generated. If the ESR is too high, besides limiting the available surge capability, you will experience excessive internal heating, which is often the cause of premature failure.
"I did buy the Hipster PSU (exppecting it to be good quality) just before I moved into my house so it could be that my house has vast quantities of dust which are not friendly for PSUs".
While the excess dust may have been a contributor (and a good reason to consider a case with a removable, washable air filter) the THG review you cite should have served as your caveat emptor notice. :-)