I have a Niro EV, and right now I'm using a portable level 2 charger on a 240v/16A circuit. I may upgrade that to a 40A circuit at some point in the future, but at the moment, the 16A is sufficient.
Are there any OpenEVSE chargers that support 16A and 40A charging (if I look in the shop, I only see 40A and 50A)? And if so, is it hard to switch the configuration? Also, I have a NEMA 14-30 outlet... will I need an adaptor?
The 40A listed is a maximum, the OpenEVSE Advance Stations includes WiFi, it is very easy to set any current from 6A up to the maximum. You will not need an adapter, the included plug fits NEMA 14-30, 14-50 and 14-60.
In addition to the above, note that there's a 48A version of the OpenEVSE available in the store as well, BUT - and this is a big BUT - the charger in your Niro EV is only a 7.2kW AC charger. This means that it will top out at around 30 to 32 amps. If you buy anything beefier than that, you're not going to see any advantage with your current vehicle. Future vehicles may support higher AC charge rates, but for home charging, 7.2kW / 30A is very respectable. If/when you buy some new future EV and if it supports higher charge rates, you could upgrade the contactor and cables in your OpenEVSE at that point but if it were me, I'd wait and see how you go, first. You might find that you don't have any great need to go to higher amperage and if not, why spend the extra money on heavier cabling that's a pain in the butt to work with, heavier contactor, heavier circuit breakers, etc.