In most installations, the eGauge (not to be confused with the HomePlug adapter) is powered directly from a circuit breaker or breakers. In your breaker-panel, locate the breaker to which the eGauge is wired. This breaker should be labelled "eGauge Disconnect" or something similar. In a residential installation, it is usually a two pole breaker (similar to that used by a stove or dryer). In buildings with three phase power (typically large commercial/industrial settings), it will be a three pole breaker. Some services outside the United States may only use a single pole breaker (single phase power).
Once you locate the breaker, trip it so power is off, wait 5 seconds, then turn it back on. Normally, there is a single multi-pole breaker for eGauge, but in some cases there may be two or three separate breakers (one per phase/leg). In the latter case, turn off all eGauge breakers, leave them off for 5 seconds, then turn them all back on.