5 V 2 A Power Supply with a microUSB Plug

It all started when the power supply for my old tablet began acting up, so I decided to find a replacement. I found one with the familiar plug and a non-detachable cable.
I’ll probably repair the old power supply—I’ve already thought of a use for it—and today I’ll try testing the new one.

I’ll try to keep this review short and to the point. As always, there’ll be tests, a teardown, and an analysis.

I’ll hide the packaging under a spoiler; there’s nothing interesting there anyway.

The power supply is fairly small, and looks like a scaled-down version of the popular 12 V 2 A models.
The cable is about 1.4 meters long. Personally, I’d have preferred it to be half that length.
A few things made me happy.
1. It really does have a European plug, not an adapter included in the box.
2. The cable is non-detachable. Extra contacts don’t do anything to improve reliability.
3. I bought this power supply for a u9gt4 tablet. It has an aluminum case, and not all plugs work properly with it. I haven’t found any problems with this one.


I think it’s obvious that a power supply review without tests isn’t a review at all, so I put together a small test setup.
It consisted of:
Electronic load + a power supply for it
Oscilloscope
A microUSB socket with a wire soldered to it.
And, of course, the power supply under review

Some readers will probably say that the voltage should be measured at the power supply’s output, not after the cable. But here’s how I see it: since the cable isn’t detachable, you can’t replace it with a better one, so it’ll be used exactly as it is. That’s why it should be tested that way, too.


First test: no load.
The output voltage is a little high. I’ll explain why later, but I’ll say right away that this was intentional.


Ripple was measured with the oscilloscope probe set to 1:1.
Ripple at no load is pretty rare, so everything looks fine here, too.


Next are four tests at different load currents. They also give you a good idea of what an electronic load is and what it’s for.
Test currents:
0.5 A — voltage is within spec.
1.0 A — voltage is within spec; ripple is almost the same as at 0.5 A, measuring 90 mV.
1.5 A — voltage is still within spec, but ripple is clearly higher now, at around 120 mV.
2.0 A — the voltage has dropped significantly, and ripple has increased to 150 mV.
I wouldn’t say the ripple voltage is extremely critical, but I’m not too happy with its shape.


And here are the oscilloscope traces.


Ever since the days when the 155 and 555 series logic chips were common, I've been used to thinking that as long as the supply voltage stays within ±5% (for 5 V), everything is fine.
So I decided to find the maximum current the power supply could deliver while still staying within tolerance.
The measurement showed 1.71 A, even though the power supply is marked 2 A.
But in reality, this is probably less the power supply's fault than the cable being too long. That's exactly why I regretted that the cable was so long.


After that, I ran the power supply at 2 A for about half an hour and measured its temperature. It was plugged into a wall outlet with the cable pointing down.
The hottest spot was just below the middle of the power supply, where the case temperature reached 62.2 degrees. At the top of the power supply, it was around 55 degrees.


During testing, I tried connecting this power supply to my tablet and saw a familiar problem: “phantom” touchscreen touches.
It looked like this:
You touch one spot, but the response registers somewhere else.
One touch produces several responses
When you press and hold, a horizontal line of visible “phantom” touches appears. In other words, right-clicking (pressing and holding) is simply impossible.
All the glitches were along the horizontal axis of the screen.
Although I hadn't bought the power supply for this tablet, I decided to try to figure out the problem.
And as everyone knows, any investigation starts with taking things apart :)

Based on the tests above, the teardown, and my attempt to modify it, I can give a pretty good rundown of this power supply's pros and cons.
Pros
The power supply has a European plug, not an adapter
The circuit uses a dedicated PWM controller
The cable is permanently attached (although in this case that also turned out to be a drawback)
The plug fits securely in the tablet's socket, even when the socket is recessed into the case.

Cons
The touchscreen may have problems on some devices.
No input power filter.
The capacitors have too little capacitance, and the transformer is undersized.
There is a large voltage drop across the cable because it is long and its conductors have a small cross-section.

My opinion: If you consider it simply as a power supply, it can work quite normally up to 1.5 A, without overheating or voltage sag. But at higher currents, the voltage will drop below the acceptable range. The cause of the touchscreen interference is also unclear, but the problem is real and obvious, even though the output voltage ripple isn't all that high.

I don't know whether this review will help anyone, but I tried to show in as much detail as possible what this power supply is like.

The product was provided for review by the store.