Why would I need to use the 24VDC adapter when using the APC Isolated Extension Cable?
"When attempting to connect a system running PowerChute plus in simple signaling through an Isolated Extension Cable (IEC), you must use a 24VDC adapter to power the UPS End Unit of the IEC.
The server side is powered off of the serial port itself. Therefore, the DC adapter is not required. This adapter is available for purchase on APC's Web site (www.apcc.com). Users may also find an equivalent power adapter at their nearest electronics store. The specifications for the 24VDC adapter follow: