Dissecting an Aliexpress Scam

By Nulltek

Its not unusual to be thoroughly underwhelmed by the performance of any electronics acquired via aliexpress. The sellers often take some pretty optimistic liberties when it comes to performance specifications. This “12V 6A” switch mode power supply I purchased was no exception, I was curious, perhaps if I could even get 36W of power out of it it’d still be a bit of a deal.

My first clue that that the whole charade was a joke should’ve been the sellers photos, which as the current rating increased just showed a bigger image of the same power supply. I suspect they at least have the courtesy to place a different bogus sticker on the “higher rated” supplies.

I didn’t even need to open the parcel to know there was no way this thing was source any decent load, it weighed about 100grams, cable included. I figured I’d test it out anyway, so I connected a series of power resistors as a test load. The plan being to determine how much current I could draw before this thing began folding back the secondary voltage or became an active insurance claim. No surprises, beyond 1A the supply becomes essentially useless, a far cry from the 6A claimed by the seller.

So may as well crack this junk open and have a look at what my $8 gets me. I figured I may as well find out if this thing is even safely designed for 1A constant current draw. It was disturbingly easy to open, as I was able to pop it open without using any tools. This revealed the internals in all their lack of glory.

A single sided PCB, literally held in place by one tiny strip of double sided tape. This PCB containing a pretty minimal design for a class 2 unearthed switch mode power supply.

The good:

  • There was actually a reasonable amount of capacitance on the secondary side (~800uF total).
  • There was actually a full bridge rectifier present, rather than just a single diode.
  • Decent primary secondary air gap, at least 9mm of un-breached separation.
  • At least there is a snubber network on the switch for some form of EMI suppression.

The bad (terrible):

  • False earthing pin, I hate this.
  • There is not a single heat sink or spreader in sight.
  • The isolation capacitor is not rated for Y2 operation, which is a potential safety hazard.
  • The bulk capacitance on the primary side is definitely on the light side.
  • There is no fusing at all, no spark gap between the primary secondary either.
  • The build quality is terrible, the soldering is barely passable, most of the components aren’t seated correctly.
  • There’s nothing to bleed the bulk capacitor, and no inrush protection, likely the potential for a bit of a shock on the input pins (fortunate they cheaped out on the capacitance in this case.

It’s a dicey lottery buying parts off ali-express, there’s a reason the prices are cheap and when it comes to anything operating on mains, your safety is definitely worth more than the cost of upgrading to a decent power supply. Never again!