For years I've always built cheap systems believing that there is little difference in more expensive components when it comes to reliability and quality, I generally believe this still except for Power Supplies.
I've always bought cheap cases with nice sounding 350-550W stock/cheap/crap power supplies and haven't had any issues for the most part until recently.
One such case is an NGEAR case with a 550W Optimax power supply, I always read that these supplies don't produce the stated wattage in many or most situations but never had any issues, at least years ago with Geforce 64MB add-on cards etc..
My first run-in that I know of with a bad power supply or one without enough wattage was when I had 4 hard drives running off a single rail of another cheap NGEAR case with the 550W Optimax PS, one of the drives would keep resetting constantly and I thought it was a bad drive, but then I realized every drive plugged into that socket had this issue. It turns out it wasn't getting enough power especially with multiple RAID 1 arrays running off it (using another rail solved it and confirmed it was a power issue). In the same case but with a different motherboard I used to run a Geforce 7300GT which kept crashing my computer after a few days, I'm confident it was a case of the power supply crapping out after extended use and being able to supply enough voltage.
Now with my other Desktop, using the same case and 550W Optimax I ran the same 7300GT for a few days but it would keep getting hotter (this is because the fan on it never worked) to the point that it smelled like battery office in the office. It would also easily hang if I tried overclocking it and my system would often lockup with it.
Eventually I decided to upgrade to a Geforce 430 from Asus because it was a great price but this card would crash after a few days but I believed it was a bug with the NVIDIA Linux driver. I also noticed my power supply getting very hot (pushing more hot air out than usual) and eventually a screeching/metallic/whirring/buzzing noise which I just thought was the Asus fan on the GPU. A few days later my computer was powered off on it's own, and it wouldn't stay powered on for more than few seconds. I removed the NVIDIA card and booted with the on-board ATI and it too wouldn't stay on for more than a few minutes. I knew right away it was the power supply for sure.
The solution was to buy a cheap but on-sale Antec 450C 450W 80 Plus certified power supply. This is where I'm happy and wiser because I didn't realize 80 Plus means 80% efficiency, versus the the likely 50-60% efficiency of crap power supplies. This new power supply so far has kept me running stable for over 3 days,no crashes yet and is almost 100% silent and runs much cooler. My GPU even reports at being 57-58 degrees on average verus the 60+ temperatures with the old power supply. This is how much more efficient and cool the Antec supply is running. On top of that my office will be cooler in the summer, I'll save energy and things are much more quiet. It has me tempted to have all the power supplies in the office and at home swapped for high quality units.
I've also read/learned that the cheap no-name units are basically rejects and are known to be of low quality which is why they are priced so low. They may serve an average user fine but if you start adding hard drives or modern video cards, you'll definitely have issues.
I'm also just glad that my dying/bad power supply didn't fry my HDDs or MB as I've heard of it in some cases (even though some including techs claim this isn't possible when it clearly is).
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