APC Rack PDU (AP78xx, AP79xx, AP86xx, AP88xx, AP89xx) and 2G Rack Automatic Transfer Switches (AP7752, AP7752, AP7730, AP7732, AP7721, AP7723)
Compatible with APC part 940-0144A ​
RJ12 to DB9. Compatible with Rack PDU (AP78xx, AP79xx, AP86xx, AP88xx, AP89xx) and 2G Rack Automatic Transfer Switches (AP7752, AP7752, AP7730, AP7732, AP7721, AP7723). APC part 940-0144A
APC pins 1 and 6 are usually not connected
Set 9600 bps, 8 data bits, no parity, 1 stop bit, and no flow control to communicate.
Apply the port settings to establish the connection.
Press 3-5 times to display the username prompt.
Use the default username and password of apc

It is possible to use RJ11 plug that has only the middle 4 pins (2,3,4,5). connected APC pins 2,3, and 4 only and it workes perfect.