See Real-Time Power Consumption in Ubuntu’s Top Panel
Quoting: See Real-Time Power Consumption in Ubuntu's Top Panel - OMG! Ubuntu —
“Why would I want to see energy usage?” – anyone asking that question probably doesn’t.
This is more for the curious folk, those interested to see the relative power demands of software being run, the tasks performance, hardware settings, devices connected, and so on – think educational rather than essential.
Of course, anyone can monitor power consumption on Linux without an extension. Command line tools like upower can do it, as can some system monitors, and there are dedicated GUI energy apps, like Power Statistics which is included in Ubuntu.
However, what the Power Tracker GNOME extension offers is a more ambient way to see energy consumption without being focused solely on it. No need to keep an app running and in view, or switch to/from one to check the readings.