Actually is possible for two of your power supplies to be weak and on not weak. If poor quality component were used in the manufacturing of the power supplies they will not be consistent in performance from one to another. Electronic components have specs to certain tolerances.
You can buy many different resistors with the same value, but different ratings for the acceptable range of variation. 20%, 10% 5% and even 1% you pay more per piece for the more precision rating. The same with capacitors many may be rated the same for voltage and other ratings but have different heat tolerances. If the temp exceeds the specified tolerances the loose efficiency and can cease to function. This applies to almost every electronic component used in manufacturing a power supply.
As an RF Engineer (radio engineer) I had to be very careful with the specific parts and their tolerances as these parts were used to generate and control frequencies. We had to stay on frequency and within a very narrow margin of power output. Every part was exposed to rf and heat. There is much more involved in how parts react to these factors than I can explain in the response.
It is true you get what you pay for, these factors stated above are why some power supplies are more efficient and more reliable than others. These Chinese power supplies are very cheaply built and do not use high quality, precision parts and that is why they are flakey and unreliable.
I am sure there are others here who can vouch for what I am saying, if you desire take some time and do some research and you discover what I have said is true. If your one Chinese power supply is holding up, it means you were lucky and got on that exceeds the average!
Mtnminer
Having similar fan problems with 2 of my 3 with factory standard PSU. However as there is one machine running at full speed, I'm amiss to think that the PSU's cannot provide enough power, as the 3rd one wouldn't mine at 200Ghs+.
Even taking the chip frequency down to 300 doesn't cause the fans to start.
Strangest behaviour is that from a cold start, machines and fans work fine. Problems start once they reach working temperature.
What fan speeds are you seeing on your units. I am getting 2880 rpm on the upgraded power unit running at 1500 mhz. My other three units with the factory power supplies just can not keep the fan speeds up and I an running them under clocked until my other eight upgrade power supplies arrive. They are all running fan speeds at about 2280 rpm, if I raise the mhz the fans speeds drop and eventually quit due to the weak factory power supplies! One is still sitting cold just our of the box, waiting for the power supplies to arrive.
Mtnminer
Just wondering what is the best setup of fan speed that everyone is going for ?
Me after 3 weeks with my machines, the best combination for me is:
Chip Frequency(Default: 300) 1300 or 1400 (1500 drain too much energy, and increase the % of error too much so no point…
Target Temperature: 65
Overheat Cut Off Temperature: 75
More Options(Default: —quiet): --avalon-fan 20-20
These setup are giving me:
Temp1: 25
Temp2: 65
Temp3: -1
Yep, there's no way you're going to be able to run at 1500 with those temps at that fan speed. If I don't do anything to the fan speed, I'm at 29 and 41 and I can run 1500 no problem with about 4% error, which is perfectly fine.
