Tag Archives: psu

Another Power Supply rant…

So, here’s a rhetorical question: What voltage/current curve is to reasonably expected from a rated power supply? (Note: I already ranted about a couple of 5V 2A supplies that failed to deliver, hence the “another” in the title.)

Your would think that I’d learn by now and shouldn’t be so pissed off when I test a power supply only to find it to deliver just a fraction of its rated performance. Case in point: I just took delivery of a rated 12V 1A switched-mode power supply (wall wart) that I bought on eBay. I plan to use it to drive a string of RGB LEDs so really wanted to get at least 0.7A at a supply of around least 10V – basically asking for about 7W, approx. 60% of its rated power delivery.

So, another rhetorical question: Is this an unreasonable expectation for a switched-mode power supply?

12V 1A "Wall Wart" Switching Power Supply

12V 1A “Wall Wart” Switching Power Supply

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Cheap 5V Power Supplies: severely over-rated!

I just received another couple of 5V 2A power supplies from China, purchased through eBay, for $2.70 CDN. Not a bargain, but a good price! As per normal, I tested them to ensure they are useable and was very surprised to find that both were completely sub-standard and unusable. The first had an open-circuit voltage of 4.5V and this fell to 4.0V under less than 1A loading. The second, with an open-circuit voltage of 5.1V, fell to 2.5V under the same resistive load of 900mA. So much for the 2A rating!

5V 2A Power Supply Unit

5V 2A Power Supply Unit

I informed the seller and he has agreed to provide a full refund. However, if there is a point (moral) to this story, it is to test everything you receive on eBay before leaving feedback!