I own a number of 240V AC -> 12V DC power supplies, obtained for different projects or to power appliances. Notwithstanding the maximum output amperage, are there any straightforward methods (short of dismantling) of determining the design and/or component quality for each unit? By "quality", I refer to efficiency and reliability of operation.
Below is a photograph of several units that I have, in case there is some relevant information displayed on the casing:
You can compare the approval file numbers with those listed on (say) UL's website. If there is no file number on the device it may be dangerous. If the file number is there, and matches a plausible manufacturer, however, it may still be counterfeit.
For safety you could test with a HiPot tester for isolation between mains and output. This can be destructive (to the adapter), if the test fails.
There is no way to tell from the outside if the device is reliable or might put damaging (to whatever is connected) voltage at the output. It's less likely that it would be dangerous to humans etc. if it passes the HiPot, but there are still ways of making adapters dangerous and pass- for example conductive debris rattling around inside or the use of substandard and unapproved Y capacitors (the latter bridges the mains and output so is part of the isolation barrier).
Efficiency is quite easy to measure- if you have the right equipment. Measure the true power input with various (and no) loads attached. The load can be a simple power resistor but it's easier to use an electronic load (and you can automate testing at various loads). You probably also want to know the output ripple and load regulation, which can be done with a multi-meter, and/or oscilloscope or spectrum analyzer if you need to know more information). With an environmental chamber you could test the regulation and efficiency (and functionality) at various temperatures.
You could even get some idea of expected lifetime by doing accelerated life testing at high temperatures.
Rip off those black cases, and direct airflow at the circuitry. The lifetime becomes near infinite.
I'd say it depends on the level of trust you have in the manufacturer.
Yes, all of this happens in €2 chinese USB chargers, and the only way to know is to open them and have a look.
A multimeter or oscilloscope and a variable load can be used from some tests. To check for ripple, noise, voltage and current accuracy. Efficiency can be checked by measuring the input vs the output. Short term Reliability over time can be measured at multiple temperatures over a few days, but long term reliability cannot. A visual inspection of the parts and circuit board is the quickest way, short of buying from trusted sources.
There is no simple way to prove good quality. It must be verified in large numbers with a rigorous DVT plan. ( 10 to 20 random samples. )
But is easy to do a tear down and observe quality design components and design principles and measure temp rise , ripple dropout level load regulation, stability with a step load response, input power efficiency to make an educated guess.
You can rarely forecast high quality from 1 sample unless you are using trusted brands like Murata-Lambda or high volume producers like Bang-Good.
