AC adapters draw power continuously whenever they are plugged in, even when not actively charging a device. A plugged-in adapter draws a small amount of idle current to maintain its internal circuitry, typically ranging from 0.1 to 1 watt depending on the adapter's design and quality. This "phantom power" or "standby loss" contributes to electricity bills and environmental impact over time.
When actively charging a device, the power draw increases significantly—often 5 to 20+ watts for phone or laptop chargers. The actual consumption depends on the adapter's output rating, efficiency, and whether the connected device is drawing at full capacity.
Modern adapters are generally more efficient than older designs due to improved electronics and regulations in many countries requiring minimum efficiency standards. However, older or lower-quality adapters may waste more energy as heat. To minimize idle power consumption, you can unplug adapters when not in use, use power strips with on/off switches, or choose high-efficiency certified models. The cumulative impact of leaving multiple adapters plugged in throughout a home or office can be measurable on annual electricity usage, particularly in buildings with many devices.