Do AGM's charge quicker?

To use a constant voltage power supply as a charger it must have over current protection, preferably constant current protection. The constant voltage is a setting, when attached to a discharged large lead acid battery it will attempt to supply set constant voltage, immediately hit over current protection and go into constant current mode with voltage dropping accordingly. This is bulk charging. As battery charges the voltage to maintain max power supply output will rise until hitting power supply constant voltage setting, at which point current will be lowered to maintain set voltage. This is absorb charging. Congratulations you have a two stage charger, just be sure to turn it off after a while or lower it’s constant voltage setting to float voltage for a manual third stage.