* The wifi access point is no longer visible to laptops and other access devices.

Double check if the power supply still works. Use a multitester to check for absence/presence of power. If your site is using a Mikrotik router (Metal 2SHPn Wi-Fi hotspot Access Point), note that its power adapter has 24 volts 0.8 ampere rating.

the power supply connects to the access point via a PoE (power over ethernet) injector.

When confirmed that the power supply is dead, buy a replacement power supply with the same power rating. Stores like Lazada and CD-R King may carry such replacement item. A variation in terms of amperage (say 1A) can also be a replacement. You may have to use the end jack of the line from the old dead power supply if the new one doesn't fit. Note of the polarity and be careful not to mix up “+” and “-” Maintain polarity from the old power supply.