I have the power brick Micro Center recommends, with a 5.1 input. Everything else runs with no low power symbol. Lakka just shows the symbol on a black screen.
Install the latest RPi3 stable Build
Following the next step of the guide using etcher.io tool
Lakka 2.1 gave me the same issues you did. downloading the latest stable build of 2.2 worked for me on my RPi3B+