Bests & Worsts Reviews from Amazon

As an electrical engineer I decided to test this power supply with an adjustable DC load to see if it could actually live up to the manufacturers specifications (5V@3.5A) and would be useful for a Raspberry Pi 3B+. You see a lot of cheap, poorly built power adapters for sale on Amazon that, not only can't supply half of what they claim, but are potential electrocution and fire hazards as well! You also see supplies that, while well built, still don't make for good Raspberry Pi 3 power supplies; this class of supply can deliver the rated current, but does so at the minimums of the USB specification (4.4V). Thankfully, this supply *doesn't* appear to be in either category! While I haven't physically opened up my unit, I can tell by the amount of noise, ripple and switching artifacts that they're using a decent design with proper output filtering (which is usually the first thing dropped on cheap supplies). I've uploaded two photos to my review. The first one shows PWR+ adapter and test setup, the second shows voltage and current waveforms from the adapter under various loads. In that image the first 3 rows and columns show the current and voltage waveforms from idle to 4A, in 500mA steps. The last two shots show a closeup of the voltage waveform (AC coupled, 20mA/div) at 3A and 2A loads, respectively. As you can see, the adapter does well with loads all the way up to 3.5A. While, overall, the switching noise is on the low end, there is a noticeable increase in high frequency noise with loads greater than 3A. However that's not unexpected nor a big deal. If it's an issue for you (using your Pi as a 384kHz/32-bit DAC, for example) the noise can be negated by attaching a snap on ferrite choke (RF filter) to the microUSB end of the cable. (I keep a dozen or so 13x25.2x3.5mm filters on hand specifically for attaching to the ends of AC adapter cords.) I also tested the supply under burst conditions (5A 1us pulses on top of a sustained 1A load, which simulates a SBC such as the Pi doing brief, intense I/O and processing operations) and the adapter was able to cope without more than a 100mV drop in voltage. With pulses longer than 10us the supply starts sagging quickly, which is expected as it's the output capacitor of the adapter that supplies this current and once depleted the adapter is unable to cope with the load. Burst tests at 3.5A or less showed favorable results. The only test the adapter failed was when going from no load to full load. In those cases there is a period of around 100ms where the voltage declines before the adapter catches up; this is due to the adapter operating in pulse skipping mode at low loads. It's only a minor point but worth mentioning. Finally, I did a burn-in test, running the adapter at 4A for 24 hours. It survived fine and didn't heat up by any appreciable amount. I should also mention this supply *does* indeed contain over-current protection, which seems activate at 4.5A. For those of you who don't have engineering degrees, the gist is this: The supply delivers 3.5A at just over 4.65V, which is more than enough to power an *overclocked* Raspberry Pi 3B+ plus attached USB devices and fan, *without* any of the dreaded "lightning bolts" appearing. To be honest, 3.5A is really pushing the limits of the microUSB connector.^1 That's your bottleneck, as the contacts are so small they add appreciable resistance, which lowers your voltage as the current increases.^2 Finally, the build quality of this adapter is very nice. It has a solid feel, with no creaking or flexing when squeezed like you get on cheap adapters. The cable itself appears thick and has strain reliefs on both ends; the microUSB connector also appears to be of the higher quality variety. All in all I'd say this is a winner for the Raspberry Pi 3B+ or other high powered SBCs; it's cheaper than the official adapter and provides more current. Likewise, for non-SBC uses (charging phones, tablets, etc.) this should also work great. ---- ^1 - This is why USB-C doesn't deliver 5V, but instead supplies a much higher voltage at a lower current, which can then be stepped down to 5V at a higher current on the device itself. The reason smartphones and tablets can get by with microUSB at higher currents is that they don't need more than 4.2V or so to charge their batteries, so they can deal with the voltage drop. ^2 - Frankly, if your Pi (or other SBC) needs more than 3A you're much better off getting an adapter with a male 5.5x2.1 barrel connector on the end of the cable and then wiring up a female socket that plugs into the 5V and GND pins of the GPIO header. (In that case, be careful! The GPIO pins have no reverse polarity protection!) *Edit 01/20/19* I have two of these supplies that have been going strong since August 2018 and am about to purchase a third. :) One thing I did forget to mention in my initial review, the microUSB connector: Another reviewer mentioned issues with his microUSB connector breaking after a year, however he was using the supply with a tablet, so that’s to be expected. A microUSB connector is only rated for a few hundred mating cycles at the most. Most Pi users will only disconnect/reconnect a few dozen times (assuming the Pi is used for a set purpose, like a media player or emulator) so that’s something that shouldn’t be an issue. If you use your Pi for experimentation and need to turn it off and on a lot, I’d reccomend getting an in-line microUSB power switch, or unplug the adapter from the wall instead of unplugging it from the Pi.