This is what I use
https://www.frys.com/product/9523082?site=sr:SEARCH:MAIN_RSLT_PG I got it for $60 when it was half price, which was almost a no-brainer, it now appears to be that price again. I've been very pleased. I would test it and give you an accurate picture of performance, but my wife has borrowed it for a few weeks and it's not in the US with me - she's got a Dell XPS 13. From memory, the Go seemed to charge a bit quicker than the supplied charger and around the same as a Go charged by a Surface Pro charger.
PD is a revelation, it's totally transformed the ability to use the Surface Go for me, it's certainly the first time I've found a good reason to search out any future purchases with a USB-C port with charging capability.
I also have a Naztech device with power socket built-in, this doesn't charge the Go via USB or USB-C, but does work with the power pack, which was why I bought it, not being able to charge the Surface Pro with USB-C.
As with all these sorts of things, I've had good experience with Naztech, but others haven't so just consider that, although since the cells used in these battery packs probably all originate from the same Chinese factory, I'm not sure any one manufacturer is more reliable.