I'm confused. Since iPhone 12 Pro doesn't come with a charger, does that mean I can safely use *any* USB-C charger?(such as Samsung S9 or Google Pixel 3 USB-C chargers)
Obviously I won't be trying it with some random no-name charger...
Any charger made to spec will work. Just keep to the big well known brands and stay away from cheap stuff and it's perfectly safe.
Cheap chargers are often nor properly designed and can damage the device by their insufficient filtering and voltage stability, cause fires due to underspecced components and poor fire protection, and pass live current through due to poor isolation which can be very dangerous.
For me, I wouldn't bother with buying a usb charger that's less than 60w. RAVPower sells a really small one for about $24. I can than use it with any of my devices, from iPhone to my MBP 13". I like the idea of being able to grab a charger and usb c cable and know it'll work with everything.