I wonder if my system is good or bad. My server needs 0.1kWh.
Joules (J) are the official unit of energy. 1W=1J/s. That means 1Wh=3600J or that 1J is kinda like “1 Watt second”. You’re right that Wh is easier since everything is rated in Watts and it would be insane to measure energy consumption by seconds. Imagine getting your electric bill and it says you’ve used 3,157,200,000J.
3,157,200,000J
Or just 3.1572GJ.
Which apparently is how this Canadian natural gas company bills its customers: https://www.fortisbc.com/about-us/facilities-operations-and-energy-information/how-gas-is-measured