Your phone will take longer to charge if the charger doesn’t provide enough power. Or all lowcost chinese chargers are worthless? The problem is, you’ll never supply the startup-current of a few capacitors on the output this way. The iPhone charger performs extremely well at filtering out spikes and noise, the best of the chargers I measured. Thank you so much for posting your findings! Did you just splice a multimeter into the USB cable?

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Second, don’t buy a counterfeit charger; the price is great, but it’s not worth risking your expensive device or your safety. It’s pretty dodgy – there’s no isolation gap between the primary and the secondary. The example is specific to CPUs but the idea holds for any power source and load.

Thanks for your help, Andy. Why V in trains and V normally? I have several brick type power supplies that I’m thinking of converting into “usb chargers”: Ironically, after computing these detailed power measurements, I simply measured the input current with a multimeter, multiplied by volts, and got almost exactly the same results for vampire power.

There are lots of comments about testing brand Bb and aaaa.

Lightning Cable

My initial thought is that Apple “programmed” it that way to discourage 3rd party accessories. Apple uses proprietary mohorola on motkrola middle two pins to indicate that it’s an Apple charger, and HP uses different voltages to indicate that it’s an HP charger. Also looking at the oscilloscope traces I suspect that not only was this tested only for V but also only at 50Hz. Finally, Regulation shows the overall stability of the output from the charger.


Monitor Cable

Apple is very good, but not motirola the best. The pulses are smoothed out with filter capacitors before being fed into the switching circuit, but if the filtering isn’t sufficient the output may show some Hz ripple.

Also, could you make one graph that shows the voltage output, versus amp draw, of all the power supplies. A 10W charger must have under. The US plug isn’t grounded, but in other countries the lack of ground in the counterfeit could pose a safety hazard.

What is your view? The spectrum orange, left is much higher everywhere, indicating noise at all frequencies.

I would be interested to see a wider range of chargers tested, as manufacturers even the good ones seem to provide little information on their products ffoxlink nominal input and output figures. Thank you for the great article on usb power supply. This output is not something you want to feed into your phone. But more importantly, these chargers ignore safety standards. I’m sure you have been getting requests for years but have you looked at the Anker 40w 5 port charger?


The yellow line is relatively thin, showing good regulation. There is no reason for a powersupply to HAVE a constant-current mode. Charging your device with one of these chargers will be a slow, frustrating experience.

Despite being very similar to the Apple charger on the outside, the Samsung charger uses an entirely different design motorlla circuitry internally. I recently purchased a USB wall plate http: So the author should have tested first if the charger was a standard USB-charger or Apple-crapped. Motorolw really popular on amazon and has a lot of reviews but it would be great to have the technical details to back up their claims. What would be helpful is a second analysis focusing on carrier and phone manufacturer branded chargers.

A dozen USB chargers in the lab: Apple is very good, but not quite the best

Please use this form to contact us. The “voltage sag” in the Apple adapters is a common technique.

Name-brand chargers use a specialized control IC to run the charger, while cheap chargers cut corners by replacing the IC with a cheap, low-quality feedback circuit.