Nintendo is getting a bit more proactive about this problem now, noting in a new Japanese FAQ page (machine translation) that users should only use USB-C cables with a 56kΩ resistor with the Switch.
When charging the Switch from a source with the older USB-A output (the boxy, rectangular one), Nintendo recommends only using the official "HAC-010" cable that comes with the Switch Pro Controller or Joy-Con Charging Grip. That cable is also available for individual purchase in Japan, but it doesn't seem to be sold individually in North America. That said, a Nintendo of America support mod recently said that "any USB cable that supports a USB Type C port should work just as well" for controller charging, so maybe being "official" isn't so important in this case.
Using non-approved or poorly rated cables might damage the Switch or prevent it from receiving sufficient power, Nintendo of Japan warns. That's a story observant Ars readers should know all too well from tales of fried Chromebooks and substandard mobile phone chargers.
And even if a third-party cable doesn't fry your Switch, it might charge the system very slowly if it doesn't carry the full amperage required by the USB-C spec. If you're really worried about compatibility, a handy USB-C power meter can give you all the details you need.
The new recommendation comes weeks after reports that some Switch systems were getting bricked after being updated to recent firmware and plugged in to third-party docks from the likes of Nyko. Nyko told Kotaku at the time that it believed the issue was related to the Switch's handling of the HDMI connection, while Nintendo simply warned that unlicensed accessories "might not work at all with our game systems, and they could have compatibility problems with certain games, the Nintendo Switch system itself, and other licensed accessories and peripherals."
