If you're looking for a bit more flexibility around the current and voltage setting as well as a more solid mounting option and safety features, take a look at fpx board [1]. fpx is open source.
There are so many USB charging standards - I had been thinking that it should be possible to construct a universal USB power converter. (Even in the case where the charger can't supply the watts the device wants, you could accumulate some energy in a small battery large cap and charge intermittently). But I suspect the reason it hasn't been done so far is liability - there are bound to be a few devices that don't play ball and blow up.
Disclosure: I'm the author
[1]: https://fpx.oxplot.com/