Separate an empty charger from charging
The adapter’s rated output, such as 20 W or 65 W, is its supply capability under appropriate conditions. It is not the power it continuously consumes with nothing connected. Charging a device, powering an accessory and waiting with an empty cable are different states.
If several ports are available, record what is attached to each. A dock or multiport station can perform additional functions and should not be treated as an empty single-port charger.
Put a tiny wattage into annual dollars
A hypothetical 0.1 W draw over 8,760 hours equals 0.876 kWh. At $0.18/kWh, the annual electricity cost is $0.15768, or about sixteen cents. Ten such identical hypothetical loads would cost about $1.58.
For comparison, a 1 W continuous load would cost about $1.58 by itself. The calculation is sensitive to the assumed wattage, so avoid reporting a precise saving from a reading your meter cannot resolve.
Understand a zero on the display
DOE’s standby measurement guidance explains the care needed for low-power readings. An inexpensive household meter may round a small load down to zero or have insufficient accuracy for the comparison. Extending the observation period can help with cumulative energy, but cannot cure every instrument limitation.
Do not build improvised mains test equipment to measure a tiny load. If a reliable measurement is unavailable, label the estimate and focus on larger, more observable opportunities.
Prioritize without overcomplicating the routine
Unplugging an unused charger may be convenient, but buying a powered controller solely to eliminate a tiny idle load can add more consumption and cost than it avoids. Use sound, compatible charging equipment and follow its instructions. For the energy budget, start with devices that run for many hours at materially higher power. Revisit charger standby after those larger loads are understood, rather than expecting a major bill reduction from a handful of adapters.
Choose your next step
Continue with the question that matches your next decision:
Sources & further reading
Numerical examples are illustrative unless explicitly described as measured. This guide does not claim hands-on product testing. Read the methodology and editorial disclosure.