A good read from MakeUseOf on USB C Charging:
The Best USB-C Chargers: What’s Safe and What’s Dangerous? - LINK
For the CTL Chromebooks, they can charge with a max voltage of 15V and 3 amps. Any replacement adapters look for a 15V / 3A (preferred) or 15V 2A. as well as a 5V / 3A option.
Google requires chargers that meet the PD3.0 protocol. Others may or may not work.
For example with the NL7/T/TW
The EC controller feedback 15V as preference output to PD on the power adaptor.
When the NL7 is first plugged in -
1. 5V output – Initial communicated preference configuration - the handshake
2. 15V output - Chromebook and adapter negotiate fix output at 15v for maximum charging speed.