I have a few SD card to USB adapters that I got from Office Depot for 9 or ten dollars. They seemed to work, but then one failed, then another. later, a third failed, so I pulled the case off to see what was going on. I was kind of surprised; the assembly was lower quality than what I would have expected.
As can be seen in the closeup photo, the metal USB connector is at the bottom, and above it are the four pins from the four contacts inside of the USB connector. The PC board has some dirt and solder around the fourth pin, and a big blob of solder is stuck to the board right under the “R11”. The third pin has a blob of solder extending from it, and nearly touching the fourth pin. A little closer and it would have shorted the two pins. The other side of the board has similar problems: solder blobs and dirt stuck to the board with solder flux. These were splashed onto the board probably from someone doing the soldering too quickly. Just really sloppy assembly.