@retropieuser555 It's the Spectrum version hacked to run on Pac-Man hardware, yes. Obviously I know I could run that instead, but I wanted to run this. Happily, I found the ROM eventually and you can indeed play it in Retropie by renaming it to pacman.zip and running it with (for example) lr-mame2003.

@shoebox low voltage can cause big problems, underclocking is one of them. I would skip the canakit power supply as they are one of the less reliable and go straight to the official raspberry pi power supply.