there is no mechanism to detect power outage and shutdown the device
there any messages shown on the console when power LED is always red?
connect console to USG 100 and collect all messages on console when the power
LED is red.
TeraTerm to open console. Baud rate is 115200.
box of USG 100, there should be one RS-232 console Y-cable.
can also find one HL-340 RS232 and connect HL-340 RS232 directly between the
USG 100 and PC.
you install TeraTerm and select the serial port?