I got Airpods Pro 2nd generation. What USB C charger should I get?

FWIW, I have a number of Apple 5W power adapters that I had gotten over the years, that I typically use for my 2nd gen AirPods Pro. I also have the Apple 20W USB-C adapter as well.

As such, I suggest the 20W USB-C power adapter for your AirPods. However, just about any quality adapter should work just fine.

as long as the charger does not output higher than 5volt DC then it should not matter

For me, if given a choice, I prefer to use Apple power adapters as their quality is a known commodity.

Although the following article is a bit dated, you may find it an interesting read:

• https://www.righto.com/2012/05/apple-iphone-charger-teardown-quality.html