I was having an issue with an older MiSTer power switch where certain cores, even the menu core, would boot intermittently. I thought it was the microSD card, but upon further research, it turns it's a voltage issue with certain MiSTer-compatible power switches. Indeed, running my MiSTer with only a splitter solved the issue.
I didn't like running my MiSTer 24/7, especially the fan, so I bought this switch at the recommendation of RetroRGB, and as advertised, it functions perfectly! All cores now boot consistently. Thanks!