Junk I Bought: My PSU Just Won’t Do

I have an Acer monitor that I’ve owned for around 15 years, and thanks to my having paid extra at the time for the model sporting a DVI socket for HDMI compatibility it still finds a place as one of my desktop monitors. It has a power brick that supplies it with 1 2V at 4.5 A, and over the years this has developed an annoying whine. Something’s loose in the magnetics, and I really should replace it. So off to AliExpress I went, and dropped in an order for a 12 V, 5 A power brick.

It’s No Heavyweight

So far so good…

These units are pretty standard, a box about 130 mm by 60 mm with an IEC socket at one end and a trailing cable at the other for the low voltage. I’ve had enough of them pass through my hands over the years to know what to expect, so I was dismayed to find when I received my PSU that it was suspiciously light. 86 g compared to the around 250 g I’d expect, so I began to smell a rat. Time for a teardown, and a descent into the world of small switch-mode mains power supplies.

Normally it should be easier to break into Fort Knox than to crack open a mains power supply, because for safety they are ultrasonic welded together. The few times I’ve done it have required some Dremel time and a bit of swearing, so when this case turned out to open fairly easily by levering with a screwdriver it was evident this wasn’t a high-quality item. Sure enough my suspicions were confirmed, for there inside was a much smaller board. It’s clear this isn’t a 5 A power supply, so just what have I received?

For A Fake, It Could Be Worse

… but not so good inside.

On the board were the components I’d expect for a small switch-mode mains PSU. Rectifier, electrolytic capacitor, control chip, opto-isolator, ferrite transformer. It’s a through-hole board, and unlike with some plug-top chargers the designer has given them plenty of space. Flipping it over and there’s a reasonably healthy 6.25 mm of physical isolation between the two sides, with an additional milled slot beneath the opto-isolator. I can’t comment on the quality of the transformer without prising it apart, but maybe it could be a little more chunky.

The board itself could even be reasonable, even if it’s in a flimsy box wired with dubious hair-thin conductors and secured only by a sticky tab. Zooming in on the chip I found a CSC7224, a little 18 W 8-pin DIP. It’s a generic chip that’s available from more than one Chinese manufacturer, and it implements a pretty straightforward switch-mode PSU. It seems to follow the circuit in the data sheet pretty closely except for the mains filter, meaning that it’s probably a working and not scarily unsafe 12 V supply module. If I needed one good for 1.5 A I’d be happy.

So I’ve been taken for a ride by a supplier on the other side of the world, and for your entertainment and edification I’ve turned it into a Hackaday article. Props to AliExpress for this, when I raised a dispute with photo and description of the hardware they did a no-questions refund. What can I take away from this, other than a warning not to play random PSU roulette again? The first thing is that, from the point of view of the manufacturer, it’s too cheap even to be a successful fake product. If I can tell by its weight that it’s fake the minute I pick it up then they’ve failed, so I’m curious as to why they didn’t make it a bit more convincing by putting a bit more weight in it. At least the chip has overcurrent protection built in, so it will simply refuse to serve 5 A rather than burst into flames.

Thus I’ve opened myself up for ridicule in the comments, and evidently I should have shelled out a little bit more. Have any of you ever been ambushed by a fake PSU?