firstly, haveing an underpowered (cheap) PSU can and will kill components, I killed 3 gpus before i realised it was my PSU that was underpowered (first old build and i upgraded the GPU and had a cheapo 550w). It caused it to spike when under heavy load which damaged teh cards. ...
Secondly, i could do all the things you have stated in your test westom, and my pc will be at about 25% cpu load, ...
Learn what Prime95 does. Maximizes stress on certain CPU intenal functions - especially using heat - as a worst case design test of that CPU. Once hot spots are identified in computer simulations, then heat generating parts (ie bipolar bus drivers) are moved to distribute heat so that timing changes cause no crashes. Prime95 mostly identifies thermal weaknesses that cause timing changes. Does nothing for what the meter must measure.
Well, I arrived when they kept blowing out graphics cards. Turns out the graphic cards were never damaged. They converted observation into automatic conclusions. One need only read specs to know why that damage did not occur. If low voltage damaged a GPU, then power off also does the same damage. When does a GPU learn power is going off? When voltage drops below a preset level. Power off or low voltage - the same circuit powers off the GPU without damage.
If voltage spikes exist, then you have numbers for those spikes. Spikes too exist because a reason must be invented. No numbers is a symptom of wild speculation and resulting myths. People who knew computers even twenty years ago know your 'voltage spikes' can not exist. Read specs that are standard even in the very first IBM PC. Internal circuits limit spikes well below what would damage a GPU. In fact, if that spike exists, then the entire power supply must lockout and shutdown. Learn about crowbars.
So when we trace voltage spikes, what do we find? Spikes cause no damage. But interrupt (interfere with) logic circuits. That would look like compete GPU failure to those using observation and speculation. For example, 0.7 volt spike on the ground pin means nothing can work ... until the missing and required sub- microfarad capacitor is installed. Just another example of how the naïve *know* something was damaged (convert speculation into knowledge) rather than first learn what is wrong.
Many computer assemblers have no electrical knowledge. Even A+ Certified computer techs need no electrical basics to be certified. Therefore many clone computers contain supplies that are missing essential functions.
Too many computer 'experts' only understand two numbers: watts and dollars. Therefore failure is directly traceable to that tech - not to assumed spikes or low voltage. Just another reason why so many computer techs ‘know’ low voltage causes damage. And, BTW, another reason why the Silicon Valley needs so many Chinese and Indian immigrants for designers.
Your post demonstrates too many ‘experts’ do not even have first semester training. Anyone with minimal training knows that anecdotal evidence only results in a speculation.
Too often, computer failures are traceable to "I speculate this must have failed; therefore this definitely caused the problem." In advanced science, your reasoning contains too much "I wouldn't have seen it if I hadn't believed it."
OP – appreciate that a majority will make recommendations without any electrical knowledge. Too many know only from anecdotal evidence – not even one semester of training. Will even attack the poster with a few generations of design experience only because they know better from shotgunning and hearsay. Even A+ Certified computer techs need no electrical knowledge to pass the test.
Appreciate how much knowledge is available to assist you – but only if you provide requested numbers from a 3.5 digit multimeter.