Some of the common causes of capacitor failure are due to voltage and current overloads, high temperature and humidity, shock, vibration pressure, frequency effects, and aging. The voltage overload produces an excessive electric field in the dielectric that results in the breakdown and destruction of the dielectric. The current overload caused by rapid voltage variations results in current transients. If these currents are of sufficient amplitude and duration, the dielectric can be deformed or damaged, resulting in drastic changes in capacitance values, and thus leading to equipment malfunction. The high temperatures are mainly due to voltage and current overloads. The overheating and high temperatures accelerate the dielectric aging. This causes the plastic film to be brittle and also introduces cracks in the hermetic seals. The moisture and humidity due to severe operating environments cause corrosion, reduce the dielectric strength, and lower insulation resistances. The mechanical effects are mainly the pressure, variation, shock, and stress, which can cause mechanical damages of seals that result in electrical failures. Aging deteriorates the insulation resistance and affects the dielectric strength. The aging is usually determined by shelf-life; information about aging is supplied by the manufacturers.
For e-caps the most common lifespan spec is the accelerated life-test of hours @ temp somewhere between 85'C to 115'C. where MTBF x2 for every 10'C drop down to 25'C based on Arrhenius Law and standard test methods.
Knowing how to verify quality means you understand what can make them fail and how to measure MTBF. It means accelerated failures with operating near rated voltage, low ESR circuits, high ripple current, high temperature, high vibration, high solder thermal shock to understand how to measure and verify if the MTBF is acceptable.
If you understand how to perform DVT's on anything and how to do failure analysis on any component down to the Root Cause and how to measure confidence levels of MTBF, then you will have begun to learn how to compare quality on capacitors.
Even the Japanese manufacturers include some mainstream lines in their portfolios, which aren't as good as their top-of-the-line products. So, in addition to the brand, we always take a closer look at the product family and its specifications to better judge capacitor quality and to make a rough estimation of their lifetime.
All Japanese caps are considered of high quality, and we like to see the following cap brands:
United Chemi-Con (or Nippon Chemi-Con)
FPCAP or Functional Polymer Capacitor (ex-Fujitsu caps segment, which was bought by Nichicon)
Besides Japanese manufacturers there are also several US and European vendors that make high-quality capacitors. Probably we won't meet any of the below cap brands inside a consumer grade PSU, at least their electrolytic offerings, but we decided that it still worth mentioning them.
Cornell Dubilier (USA)
Illinois Capacitor (Currently owned my Cornell Dubilier)
Kemet Corporation (USA)
EPCOS (TDK company, Germany)
Würth Elektronik (Germany)
On this list you will find capacitors made by some of the Taiwanese manufacturers, which often use factories in China. These caps perform well, so they are usually used in mid-level PSUs and sometimes even in high-end units, and they strike a balance between good performance and affordable prices.
Taicon (belongs to Nichicon)
SamXon (except GF series which belongs to a lower Tier)
These third-tier capacitors, according to information from various PSU manufacturers and people with knowledge of RMA statistics, along with our own experiences with caps, might not be among the best choices, but are still a grade above the caps that belong to the last category.
This group includes the rest of the capacitor brands. When you see one of these brands in a contemporary PSU, you’ll know that the manufacturer set lower-cost production as a priority instead of reliability over time. We are listing only the popular cap brands that are usually found in low-cost PSUs, but we are well aware that many other low-cost cap brands exist and there is a good chance that you'll find them in non-branded PSU, and even in some branded units.