Well, rice helps to remove the liquid. And in this case I think the coffee hasn’t even touched the PCB. Therefore removing it before corrosion happens is your best bet IF you don’t have isopropyl alcohol at hand for replacing.
Opening the power brick and cleaning it with a toothbrush (as it is suggested by ifxit for phones) isn’t a good idea for your situation as it can be later on a fire hazard with legal consequences for you.