ac failure or link failure

hey i have some question how i can tell the cause of
a switch / router went down by ac power or his links went down ?
it possible?

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Are there lights on? Are cables still connected?

Also, checking uptime will tell you how long since last power on.

"show version" will tell you the uptime of a device i.e you will know if it reloaded. Check the logs to see if a link went down, "show log".

oh sorry i mean how i can detect it from telnet /ssh