This is “reference” post for anybody else that happens to have this same very specific problem. I was looking for a way to incorporate some of the many cheap / industrial grade sensors from AliExpress with Home Assistant. Long story short: almost everything electronic in the industrial space uses Modbus to communicate, typically with a PLC. While Home Assistant does have support for the Modbus protocol, but wanted to use a PLC that could manage the sensors directly and expose the values over the network in a more standard format; MQTT.
The APC AP7900 is a 1U single phase PDU with 8 switchable outlets and a network interface. It’s been EoL’d and can be had for less than 20% of it’s original price on eBay. The network interface is so underpowered tha it can’t support any modern cryptographic ciphers. So with that, here’s a revised copy of my notes from the process of getting the device reset, updated and monitored. The Hardware Unfortunately, there’s no “reset everything to defaults” button or button sequence on the PDU.