The iPhone 13 Pro Max can charge a bit faster than other models, according to tests done by YouTuber ChargerLAB (and backed up by other tests), which show that the phone sips up to 27 watts of power when plugged into a compatible charging brick. If you have a 13 Pro Max and want to fill up its massive battery as fast as possible, you may want to look into getting a 30W charger that, according to tests cited by @duanrui1205, can charge it from zero to full in less than 90 minutes.
If you’re looking for a 30W brick to charge your Pro Max a bit faster, it’s probably worth looking around your house first: Apple includes 30W chargers with its new MacBook Air, and the 61W charger that comes with MacBook Pros could also provide the 27 watts your phone craves. You can check any other chargers in your house by reading the regulatory text that’s usually printed near the prongs — if it doesn’t outright say the wattage, you can figure it out by multiplying the amps and voltage.
This one just says it runs at 100W, so no math to do.
This one runs at a max of 18W (9 * 2), so we wouldn’t be getting the most out of it.
The classic 5W Apple charger. Please don’t use it for your iPhone 13 Pro Max.
If your search for a 30W charger didn’t turn up anything, Apple will happily sell you one. You can also find plenty of third-party ones, like Anker’s tiny Nano II GaN brick. One thing to note when looking at chargers is the charge rates they support — to get the 27W charging, the iPhone is looking for 9V at three amps, according to ChargerLAB’s video (which shows one 30W charger that’s only charging the iPhone at 18W).