I'm sure there's a smaller computer than a raspberry pi that can beat any human in chess.

It would be interesting to try to do it with the minimum possible power consumption. Would a small power-optimized ARM microcontroller such as an STM32L4 with some bulk storage be sufficient, for example? Could a device pulling < 100 mW beat a human grand master? 10 mW?

The one that beat Kasparov in 1997 could evaluate 200 million positions per second which is quite a lot. On the other hand beating me could probably be done with a modified pocket calculator.

There has been a lot of progress in computer chess software since 1997, the current version of Stockfish is very probably superhuman on a low-end smartphone

I can't find any recent experiment, but here https://en.chessbase.com/post/komodo-8-the-smartphone-vs-des... is a test done in 2014 that shows that smartphones were already clearly superhuman then

In 2019 I estimate we would need less than half of the computing power of that 2014 smartphone to achieve the same playing strength

When I was a kid I had a TI-83+ with a chess engine that could whoop my ass. Zilog z80 at 6MHz, a few KB of ram. Of course, I sucked at chess...