Two things tend to happen with tiny surface-mount packages: either the shortened device codes are undecipherable (unless you happen to be familiar with the specific manufacturer’s codes) or most of the chip code is eaten away by the wave soldering process, as in this case.
Since the transformer was connected to the board after being seated within the plastic frame, and from the other side, wire soldering had to be done in-place.
Soldering in awkward positions leads to oddly-shaped joints like the one on the diode, splatter, such as the flake you can see on the diode's body, and large blobs like the one to the right. To be fair, though, the negative terminal’s blob happens to be on top of the USB connector’s shield tabs.
Are there any major top-side components hidden by the plastic frame? The only one we spot is a 470Ω resistor nestled between the transformer and two input capacitors. There's no Y-class capacitor or common-mode choke. And we can't find a hidden third or fourth wire going to the output board. It's really only connected through those two wires.
Since there is nothing else across the input and output boundary, I will be doing my isolation breakdown test directly between the AC input and the transformer’s output wires.
Output Board – Top
USB ports dominate the board’s footprint, which is only made slightly wider to flank them with a pair of 390µF filter capacitors and a few support components that won’t fit on the back, including a lone charger identification chip.
Output Board – Bottom
With most of the back’s edge making contact with the plastic frame, very little space is available for extra circuitry. We end up with a current-limiting resistor for the LED and support components for the tiny chip on the other side.
The surface-mount diode between the two USB connectors’ pins is labeled 45R20. I couldn’t identify its brand, and mostly came up with search results for radial tires, so I’ll hazard a guess that it stands for 4.5A/20V.
ID-ing The ID Chip
When I flipped the output board and didn’t see another SOT-363 package, I wondered where the second port was getting its ID from. After a few seconds of contemplation, I figured that a six-pin chip with power and ground pins had enough leftovers to afford two pairs of D+/D- pins by omitting the CW3002’s configuration pin. One quick microscope check later, my suspicion was confirmed by finding a CW3004A, a dual-port version of the CW3002.
Photographing a translucent white subject while preserving its details is quite challenging. Thankfully, heavy contrast and edge enhancement help bring those back from oblivion, along with blemishes on my white sheet background.
The mold used to form this piece must have at least three parts: one for the bottom to form the output board's shelf, a front mold to form the recessed area above the transformer, and a back mold to form the transformer cut-out.
This may be one of the most expensive parts in there after the transformer due to its limited reusability.
Bare Frame On Base
How does this all fit together? The frame, with its two locator pins and contact arms, simply plugs into the base once all of its components are mounted onto it. Then, the whole block gets slipped inside the front housing. Since the prongs are outside the enclosure and their internal contacts are all the way out along the housing edges on the input side, no exposed prong metal comes anywhere near the transformer's low-voltage wires.
Some Pre-Assembly Required
This is likely what the adapter looks like before it's inserted and sealed into the housing. The printed board extends a few millimeters into the plug base for its contact arms to reach the prong’s contacts. Above and closer to the middle, you can see the low-voltage wires going to the low-voltage board with at least five millimeters of clearance from anything mains-related, including a two-millimeter air gap.
Short of the adapter catching on fire, the transformer is the only thing that could realistically fail and let high voltage out through the low-voltage side. Considering the amount of design effort that went into it, though, I'd be seriously disappointed if the transformer failed my withstand test.
Side By Side
Bringing one of my A1265 wannabees in for reference, the PA-U32’s transformer is roughly 50% larger in all three dimensions, making it about three times as large by volume. That's in the same ballpark as the look-alike’s whole input board. Now you know where most of the 17g difference comes from. The extra 15µF input capacitor, internal frame, and foldable mechanism must account for the rest.
By now, it should be abundantly clear that a good chunk of those extra ~$8 went into better and safer design.