Some appliances do use small amounts of power.
Instant ON, televisions have the tube electron gun always warm, so it can produce an electron stream very quickly when you press the POWER button.
An old toaster, with no other electronics doesn’t use any extra power, off is off.
Regular old light bulb lamps don’t use any extra power.
But many appliances have front panel power buttons, that are monitored by a small micro-controller on a circuit board.
When it detects you pressing the button, it pulls in a large relay, and powers the rest of the appliance. This circuit board requires a power supply, which means transformer is required across the line 24x7. This operates the small power supply, micro-controller etc. To save cost, the main power supplies needed for the appliance are on, up an running, which un-necessarily consumes power. They draw more power when the appliance actually operates, but the idle currents can be substantial.
However, many small appliances have wall transformers that operate the small appliance. The transformer itself ideally doesn’t use power, but there are losses which do cause these transformers to use some power, and I suppose it can add up. Feel the wall transformer, it is warm, due to the losses in the transformer.
You are paying for that heat.
Feel the back of your TV, or other appliances. They are probably warm, even when off.
One reason people are getting excited about this, is because of global warming, pollution, and the waste of energy.
In a house full of appliances, stoves, stereos, wall adapters, chargers, AC heating controller, VCRs, DVDs, game systems power supplies, PC sound system power supply, TVs, PC power supplies ( yes they produce constant power even when off), etc.
I would expect it to total about 100W. ~ $10 per month
0.15* (100W*24*30)/1000 = $10.80
15cents per kw times watts used per month divided by 1kW.
A transformer, is just a large coil of wire sitting across the power line. It would be a short circuit, except that the coil is wrapped around an Iron core which concentrates the magnetic field energy. It would quickly reach its maximum magnetic storage energy limit ( saturation), but the power line is AC ( alternates the voltage direction 120 times per second ( 60Hz) ). This causes the magnetic energy stored from the line power to collapse back into the line 120 times per second. So energy is briefly stored in the iron core, but a few milliseconds later, is dumped back into the line. It is designed as a resonate circuit element at the 60Hz line frequency, so the energy comes in, but goes back out in resonance. If the appliance needs power, it is siphoned off from the magnetic core, into a second winding coil, and doesn’t return to the line.
Losses occur in the resistance of the winding, and also in eddy currents in the core material that are dissipated as heat.
This is why the transformer gets warm, and why it looses power when not in use.
The core material is made of ferrite, which is iron powder mixed with Silicon, which makes it much less conductive. This reduces the eddy current losses, because to the higher resistance of the core, limits electrical current (power) being wasted in the core material. ( This has nothing to do with the electrical current in the two Copper transformer coils.)
The core is also broken up into thin slices like a pre-sliced block of cheese. The slices are insulated from each other, so that they can not sustain that current path between themselves, reducing eddy current losses. Eddy current losses increase with the square of the applied frequency, so lower frequencies are better to reduce loss for that reason. The problem is that the core then must be very large to hold enough magnetic energy to support the appliance during the slow 60Hz cycle. This means that a 500 Watt power supply may be almost too heavy for many people to lift.
For this size reason, modern power supplies are designed to "switch", and oscillate at very high frequencies ~ 70kHz, to 500KHz, so that the size of the core can be very small, but transfers that small amount of power at a much, much faster rate. It is like trying to fill a bath tub with a 5 gallon bucket of water once per minute, or using a Dixie cup at a rate of 5,000 per minute.
This means you don’t have to carry around the large 5 gallon bucket where ever you go, only the Dixie cup. Your power supply can be very, very small, yet produce large voltages, current and power. As a consequence, modern appliances are light weight, and can use almost any battery voltage. The required voltage is "switched up" or down to the needed voltage and current.
May the force be with you. . .