[PLUG-TALK] power tracing

[Randy Bush]

imagine a rack which has been incrementally 'augmented' for over 20
years and occasionally cleaned up.  some documentation has gotten a bit
out of synch, particularly which PDU outlet powers which server/router.
of course one does not want to unplug servers to trace.

is there a cheap non-disruptive gadget one can put at one end of a 110v
power lead and passively test for it on the other possible ends?

asking for a friend :)

randy