The internal fan inside the AirPort Extreme is clogged with dust, which results in decreased airflow, causing the power supply to start to overheat.
If the AirPort is less than a year old, take it into the Apple Store and ask for a replacement AirPort Extreme. If the AirPort is older than a year, but less than three.......AND......you have AppleCare in effect on one of your Macs, then the AirPort should be covered for replacement as well.
If the AirPort is not covered by warranty, your only option to solve the issue would be to open up the AirPort Extreme and replace the fan.
Parts are available here: US Stock Apple A1470 Fan US Stock - AirPort Time Capsule A1470 Fan$14.99PC Parts StoreFree shipping, no tax
Some tips on opening up the AirPort Extreme are here: AirPort Extreme A1521 Teardown - iFixithttps://www.ifixit.com/Teardown/AirPort+Extreme+A1521+Teardown/15044