I dug up my brother's old PS1 the other day, looking to play some games on it. Is it possible to play backups/homebrew without modchip or swap trick? The one game I found was scratched beyond repair and wouldn't boot.
Not really, there are some cheat cartridge with a "hidden" option to boot backups.
But for those you need a expansion slot on the back off the PSX, and those cartridges are now days hard to find.
When I got my PSX (in +/- 1998) I modded it, a friend of mine got a MovieCard (+ AcrionReplay) for his PSX.
You can play VCD's,use cheats (ActionReplay clone) and play back ups.
But for playing backups you need to do some kind of swaptrick what I remember.