Items that run off external low-voltage power supplies: Examples might include laptops (when connected to mains power), printers, etc. These devices depend upon external power supplies (nowadays usually switch-mode power supplies) to convert mains-voltage AC current to DC at the correct voltage for the device. Even when the appliance is turned off the power supply itself is still powered, and so a small amount of electricity is used by the internal electronics. This applies to USB adapters as well.
Items with low-voltage electronics that have internal power supplies: Examples include many things in today’s home, from computers and televisions to alarm clocks and radios. This category of equipment can go either way: If you turn it off using a physical switch that isolates the power supply from the mains, then it will not draw any power when off. If you turn it off using a “soft” button that interacts with the electronics, then some power will still be required by the electronics to monitor that button for when you turn it on again. Anything with a “standby” mode falls into this category, as does anything that can turn itself on at a particular time and anything that can be activated by a remote control.
Many PCs draw a substantial amount of power (sometimes up to ~15W) to not only monitor their power button but to allow wake-on-LAN, wake-on-keyboard, wake at a specified time, etc. Some computers have both a soft power button on the front, and a “hard” power switch on the rear. In this case, turning off the rear power switch will usually mean that no power is drawn while off, at the expense of disabling all the auto-on features just mentioned. Some televisions work in a similar fashion with “soft” off by the remote control, and “hard” off by a physical power button or switch – but some use a soft off either way.
Items that run directly off mains power: A simple example is a toaster: it works by passing mains current through wires to heat them; when it is off, the circuit is broken and no power is used. Equally with most bedside lamps – there is no power supply, internal or external; the bulb is connected straight to the mains and the switch that you use physically breaks the circuit, meaning that no power is used. With more complex appliances, such as washing machines, the same complication as with the low-voltage items can apply: it is not always obvious whether you are physically breaking the circuit when you turn it off, or whether you are merely instructing some electronics to turn off the lights on the front panel. Once again one can often make a good guess from the design of the switch: a “hard” off switch must physically break the electrical circuit and will thus usually have a more defined mechanical action than one that does not.
(This article is given to you be The Charlie Brown Group of Keller Williams that consists of Charlie Brown, Jena La Haye, Holly Brucks, Kay Lopez, Ignacio Lopez, Tricia Winters, Jno McGinty, Lindsey Perritte, Aubrey Kida. They are experts in the Fort Worth and surrounding areas including Fort Worth, Keller, Southlake, Haslet, Grapevine, Roanoke, Trophy Club, Justin, Watauga, North Richland Hills, Hurst, Bedford, Euless, Colleyville, Flower Mound, Argyle, Weatherford, Benbrook, Arlington, Mansfield, Springtown, Azle, Boyd, Saginaw, White Settlement, Denton, Aledo, Newark, Northlake, Westlake, and surrounding areas since 2003.)