Another 12 V power supply, but this one is rated for 1 A.

In the previous review I misspoke when I said there were two items in the package.
Today I'll show you what else arrived. I ordered this power supply for a very specific purpose, but I'll tell you about that at the end.
This review will be very similar to the previous one. If you're interested, read on.

As I mentioned in the introduction, this power supply arrived together with the first one.
But not only did they arrive together; as far as I can tell, they're also made by the same manufacturer. You can tell from the appearance, the build quality (though this PSU is a little worse) and the markings.
The previous one was marked XK-2412DC, meaning it comes in 24 V and 12 V versions.
This one is marked XK-1205DC, meaning this power supply comes in 12 V or 5 V versions. I ordered the 12 V version.

Power supply specifications.
Input voltage: AC85-265V or DC100-370V
Output voltage: DC 12V
Output current: 1A (the store listing incorrectly says 1-2A)
Output power: 12 W.
The listing also claimed low ripple, but we'll check that separately :)

As usual, I'll start with the packaging. I'll tuck it under a spoiler, as usual; there's nothing particularly interesting, so you can skip this section.

The power supply is really small, just a little bigger than a matchbox.
Its dimensions are 62.5 × 31 × 23 mm. The last measurement is the height, which could be 1 mm less, since I measured it with the transformer leads sticking out slightly.


This power supply also has an input filter and an inrush current limiter, but the filter is pared down: there's no filter capacitor before the inductor.
There's no connector either, just two holes spaced 5 mm apart.
On the plus side, the capacitor in the PWM controller's supply circuit is 33 µF, not 10 µF like in the previous one. That's good.


From another angle, you can see the output diode, output capacitors and inductor.
There are no heatsinks here, but they aren't really needed at this power level.
The diode is rated for 3 A and 100 V, model SR3100, as it should be.


And here's the first issue, and a serious one at that.
A regular 1 kV capacitor is used as the interwinding capacitor, rather than the Y1 capacitor that should be used in circuits like this.
Y1 capacitors are used in these circuits for safety: if one fails, it always fails open, since a short circuit here could have serious consequences.
I strongly recommend replacing it. You can desolder one from any switching power supply; the capacitance isn't particularly critical, but the capacitor's safety class is.


The power transistor is tucked away somewhere deep on the board, between the input inductor and the transformer. It has no heatsink and a small package, but I'll come back to that later.


As last time, here's the drawing with the board dimensions and mounting holes.


The board is very well made and assembled; I have no complaints. What's more, the manufacturer even secured the SMD components with adhesive. You can see this around the footprint for the SMD output diode, which can be used instead of a through-hole one, and on the other components as well. That's a plus.
The board is double-sided, with fairly dense components on both sides. A couple of resistors are even located under the transformer.


The PWM controller is an unfamiliar 63D39 chip. Its name is very similar to that of the 63D12 chip in this review. As far as I can tell, its closest equivalent is the FAN6862.
As in the previous review, the resistors are rated to 1% or better.


For the experiments, I decided to install terminal blocks on the board's input and output after all.
A standard 5 mm terminal block fit at the input, though I had to trim it a little near the inductor. It can also be installed without trimming (that's how it's shown in the photo).
The output holes are spaced 3.75 mm apart, but the terminal block wouldn't fit there because the output inductor gets in the way.


As last time, I decided to check the specs of the installed capacitors.
Well, these are worse. The issue is the capacitors' ESR; their capacitance and voltage rating are fine.
The capacitors are 470 µF, 25 V. The capacitance is about right, based on 1000 µF per 1 A of output current.
The ESR is noticeably high, at around 140 mΩ.


The input capacitor has the same ESR issue, though to a lesser extent. Its capacitance, on the other hand, is excellent: 22 instead of the calculated 12 (for 220 V) is very good.


First test power-up. It started without any problems. Startup takes a little longer than usual, around 1.5–2 seconds, due to the increased capacitance in the PWM controller's supply circuit.


When I described the installed components, I forgot to mention which transistor was used.
I had to practically pry it out to find out. Anything for science :)
It's a 2N60C made by Fairchild.
The transistor is a little undersized, of course, but the experiments will tell us everything.


Naturally, I drew up the schematic before starting the experiments.
The schematic isn't just for the review; it may also help anyone who buys one, since you never know what might happen. And it's good to know what to do if it burns out during testing :)


As last time, I prepared a few different things for testing.
The list is almost the same as before; the only difference is the load resistor values.
For the load, I used:
27 Ω resistor
15.3 Ω resistor, made from three 5.1 Ω resistors connected in series
10 Ω resistor (added later)
A 1 A load, which I mentioned in my review of testing batteries.




And here’s a comparison of the two power supplies. The first thing that came to mind when I saw this photo was a line from a poem by Mayakovsky: “The little son came to his father” :))


So, to sum up:
Pros
Good build quality
Very good electrical performance
Meets—and even exceeds—its stated specifications.
Price: well, it’s what it is. It’s hard to judge, but I think it’s reasonable, at least for this level of quality.

Cons
The wrong type of interwinding interference-suppression capacitor. It’s quite large, but this is an easy fix.
The output electrolytic capacitors could have been better quality, although their capacitance is fine.

My opinion: I think this is a perfectly decent power supply, even if it is tiny. Sure, its current rating is laughable—you’re unlikely to power your kitchen lighting with it—but the quality is pretty good. It’s more than adequate as a built-in power supply for some device.
I was impressed by the very low ripple, but really disappointed by the interwinding interference-suppression capacitor. It definitely needs replacing; fortunately, it costs next to nothing and is found in all switching power supplies. Replacing it is about as difficult as soldering on the input and output wires.

The power supply for this review was provided by the banggood store.

I think there are people looking for a power supply like this, as well as people who are simply interested in how these things are built, and I hope my review will be useful to them.
As always, I’m looking forward to your questions and suggestions in the comments :)