Ideally, when you buy a flagship Android device, you'll use the charger that came with the device for its lifetime. Sometimes, though, that charger may give up the ghost and a spare charger in your drawer could look like an ideal replacement. Or perhaps another device needs to be charged and your Nexus 6P or 5X charger happens to be right there. According to a video put on YouTube by Nathan K., you should resist that temptation, because the Nexus 6P charger has a strange implementation of an essential safety measure for mobile device chargers, and the Nexus 5X charger lacks that safety measure altogether.
The measure in question is a voltage control fail-safe that only lets a charger output energy when it's plugged into a device that's asking for a charge. The Nexus 5X charger, no matter what cord is plugged into it, will always output its full load. The Nexus 6P charger, on the other hand, only seems to enforce this fail-safe with its own cord. Using any other cord, smart or dumb, the charger will always output energy without being asked to. Nathan K. demonstrates this using a USB hub, a few cheap devices, and a load tester. He first plugs the 5X stock charger and cord into the devices to show that it outputs voltage when it shouldn't, then plugs a different cord into the Nexus 6P charger to demonstrate the same.
This may sound fairly innocuous, but it can be quite dangerous. Even if plugging in a device that needs a charge, the chargers may output their full voltage into a device that normally uses less and damage it. Plugging the chargers into ports that aren't for charging could likewise cause damage, and any daredevils who may even think of plugging the 5X and 6P chargers into each other should banish the thought. When the YouTuber reached out to Google for support, they were unable to help him. As of the publishing of the video, he has not reached out to LG or Huawei about the issue, so Nexus owners who still have the stock chargers could try contacting their respective manufacturer about a replacement or repair if they suffer from the same issues noted.