What the 1 kOhm @ 100 MHz means for your power rail
The ACM1211-102-2PL-TL01 is a 2-line common-mode choke from TDK's ACM series, designed to suppress conducted EMI on DC power lines up to 80V and 6A continuous. The 1 kOhm impedance at 100 MHz targets the switching noise band typical of DC-DC converters — the common-mode attenuation at that frequency is high enough to keep a 48V or 24V rail from radiating into the enclosure or coupling back onto the input cable.
DC resistance and current rating — the thermal trade-off
With a maximum DCR of 14 mOhm and a 6A current rating, the I²R loss at full load is about 0.5 W.