PSU Failure Analysis or Fault Report? FMEA or RCFA?

Engineer performing a failure analysis on a PSU.

What causes a Power Supply (PSU) or Rectifier to fail? Do I need a PSU Failure Analysis or Fault Report? FMEA or RCFA?

I hope I can help you if you are looking for answers to what caused your DC power supply to fail or to commission a professional PSU failure analysis.

Since the first UK designed switch mode DC power supply (SMPS) was manufactured by Advance in 1974, the DC Power Industry has been on a mission to make PSUs, smaller and cheaper. Some of the results have been reliable and successful, but the obsession with power density has led other vendors to create hotter, less reliable power supplies that have become just another throwaway product. The power supply is possibly the most important and often forgotten piece of equipment in your system. If the PSU fails, your equipment fails.

Fault Report.

At APS, a free fault report is available with all of our repairs. This fault report will tell you what has been replaced and an indication of why, for instance ‘ageing electrolytic capacitors’. However, if you are facing liabilities, obsolescence, expensive downtime, even danger to life and property, then you need to know more. For these situations, we offer PSU Failure Analysis and Root Cause Analysis / Investigation (FMEA or RCFA) as a consultancy service.

Failure analysis.

Starting ideally with a sample of a working power supply and a selection of failed units, We can undertake thermal analysis, a rigorous circuit design investigation and component stress study. Our PSU experts will suggest a plan appropriate to find a solution to your PSU problem.

Various acronyms are used in the industry. They often overlap and are confusing to understand. Some are not particularly relevant to the analysis of power supplies.

What Is The Difference Between FMEA & RCFA?

Simplistically speaking, it is the difference between prediction of the future (FMEA) and analysis of the past (RCFA).

Firstly, failure Mode and Effects Analysis (FMEA);  I have seen this broken down into Process FMEA and Design FMEA, but I think Design FMEA is most relevant to the study of DC PSUs, so this is what we will consider here.

FMEA is the process of investigating potential failure modes through analysis of the design. Failure modes can be simulated and modelled to see potential effects on the unit and the output. This can be used to improve the expected reliability of the unit at the design stage before manufacturing, or as part of a product change or modification.

Root Cause Failure Analysis (RCFA) is the investigation of an actual failure that has taken place in the past. It is the process by which the root cause of the failure is identified. From that information, an action plan is formulated to reduce or eliminate the possibility of re-occurrence of the same failure.

What causes failure?

Advance Product Services (APS) have studied what actually causes field failures for more than 19 years. According to our research, we have drafted a list of the PSU electronic components that are most likely to cause system failure in order of likelihood. This list may differ from what you expect, as it is specifically compiled from a study of power supplies (not general electronics), which are largely obsolete, old and have endured a demanding life!

  1. Electrolytic Capacitors.
  2. Film Capacitors.
  3. Surface mount (SMD) ceramic Capacitors.

These are real-life statistics, the results of gathering data from over 18,000 fault reports for the PSUs that we have repaired at APS so far (as of 2020).

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Why is the obvious cause of failure not always the real cause of failure?

A root cause analysis will look deeper into the reasons why a failure occurred, rather than just what failed.

To explain this in more detail, let us consider the component most likely to fail in your power supply according to our findings, the electrolytic capacitor. To understand just how it might actually have failed, we need to dig deeper into the root cause of failure. Was the capacitor specified correctly, did the circuit over-stress it? In the spec sheets, electrolytic capacitors are given a lifetime rating at a maximum operating temperature. Estimated lifetime can drop dramatically if the capacitor is allowed to exceed its maximum rated temperature, causing premature component failure.


Failure analysis finds the root cause of failure.
Close up of a failed electrolytic capacitor


A common electrolytic capacitor with a maximum temperature rating of 105C, can have a reliable lifetime of significantly less than a year when operated constantly at this temperature. Design faults in the mechanical housings, the heatsink cooling, or the circuit design  itself (ripple current) can lead to the component operating at temperatures far higher than it was designed to tolerate. Being sat on the shelf with a lack of maintenance or poor thermal management in the rack could also be implicated. So although a capacitor has failed, it is perhaps not the ‘fault’ of the capacitor, a root cause analysis will look at why it failed.

Counterfeit components

Counterfeit components can be difficult to spot. Quality manufacturers are on a constant lookout for fakes, but are cheaper repair houses so diligent?

Thermal analysis

Heat is often the enemy and thermal analysis is a great diagnostic technique, it is often the first thing our experts will use. With modern technology, thermal analysis can lead you directly to unexpected, localised sources of heat and therefore unreliability and failure in a power supply. With a working unit to undertake this analysis, dry joints, poor connections and components running unexpectedly hot can all be identified quickly.

Fit for the environment?

It is important to determine if a PSU has been operating in the environment it was designed for, so we may ask you questions about the equipment that it is installed in. A PSU that works well in a dry, dust free industrial environment may not work well when outdoors, exposed to pollution or part of outdoor maritime equipment for example. Repairing and ruggedising ultimately may be the cheapest solution for you and the best for the planet.


Finally, it goes without saying that our failure analysis studies are strictly confidential and normally undertaken with the protection of a non-disclosure agreement (NDA). This is why you will not see a Customer case study or testimonial for this service.

Want to know more or arrange your failure analysis report?

To make an enquiry about a failure analysis, please get in touch with our team