There once was something called a Super GameBoy, which was a cartridge adapter for GameBoy games to play via your SNES. It came out in 1994.

But if you wanted to play gameboy games on TV and on the go, you'd need to own a SNES, Super GameBoy and a GameBoy.

The SNES also couldn't play GameBoy games, the Super GameBoy was really just an entire gameboy in a cartridge formfactor.

But it's not the first to do that. There's a cable that allows you to connect your PSP to your TV.

Yeah, I had the same thought. However, the Switch actually makes that convenient, by design. I would play my PSP on TV all the time. It sucked. Getting the screen full size required your TV to have that option (and crappy cheap TVs didn't). Fumbling with the wires was annoying. It didnt have a stand.

The Switch has the same feature, you're right. But its designed (and marketed) around it. That's the difference.

Too small because of underscan? I'm baffled why with HDMI and the 1080p standard it's now the other way round - I need to disable overscan to get the full image and games still have to prompt me to choose a safe area to display UI elements.

You can play the PSP in your handheld and connected your TV.

With the Switch you can use it docked, handheld, and tabletop (i.e. stand alone).

Speaking of docking, there was this phone + tablet hybrid from Asus: https://www.asus.com/us/Phone/ASUS_PadFone_X_US/gallery/

Which itself is a bit silly, since there are already wireless video standards being built into TVs.

It seems like a pretty obvious ad though.

I know this counts as an accessory that bridges two devices rather than a complete device in its own right but: https://en.wikipedia.org/wiki/Super_Game_Boy. The Switch, as neat as it is, isn't without precedent.