GL-AXT1800 does not use so much power, I am getting aroung 5-6W while stressing the CPU using this [OpenWrt Wiki] Snippets.
It seems like 2 amp chargers are more than enough if you don’t plan on using USB port on the router.
Tested the following chargers:
Official Rasbperry Pi 4 adapter (KSA-15E) 5.1V 3A - works
Baseus Gan Charger (BS-3915) 65W - works
Baseus Super Si Pro (CCCJG30CE) 30W - works