Inefficient laptops and mobile phones power units are being targeted by new European Union rules that will electricity consumption. 

The new regulations, which come into force in April 2010, should lead to changes in the way the power blocks convert electricity and should make the devices themselves more efficient even when they are on battery mode, the Commission said. The regulations limit the energy that the power supplies can waste.

Despite the recent focus on eliminating "phantom power," the electricity consumed by devices in standby mode, some devices continue to waste energy even when completely turned off.

That's because they use external power supplies to convert the high-voltage alternating current from the wall outlet into the low-voltage direct current they need. Those external power supplies contain transformers, rectifiers, regulators and smoothing circuits that consume energy as long as they're plugged into the wall, even when they're not powering a useful load.

Those external power supplies are so inefficient that, if nothing is done, then by 2020 devices in the European Union will be wasting enough electricity to power the whole of Lithuania (population almost 3.5 million), according to the European Commission.

The new rules set standards for the energy that the power supplies may waste in two situations: "no load," when the power supply is powered on but the device is turned off or not connected, and normal use.

With no load, the rules will initially limit the wasted power to 0.5 watts, and in 2011 that limit will be lowered to 0.3W for power supplies with a useful output of less than 51W. That lower limit will apply to chargers for mobile phones and digital music players, for example.

While the no-load rules apply to all external power supplies, some of the less energy-hungry devices connected to them will be exempt from other regulations limiting standby power. That step was taken to avoid posing too great a burden on manufacturers, according to a Commission official.

When the device is in use, the rules vary depending on how much power the gadget requires.

External power supplies rated at 51W or more must be at least 86 per cent efficient (that is, they must deliver at least 86 per cent of the power they draw to the device, wasting less than 14 per cent).

Power supplies with an output of more than six volts must meet a slightly higher standard, 87 per cent. This is about the same level of efficiency already demanded of energy-efficient internal power supplies found in servers in datacentres.

Power supplies rated 1W must be 56 per cent efficient (or 62 per cent if the output is more than six volts). There's a sliding scale for those rated between 1W and 51W.

The new regulations have been four years in the making, and set requirements similar to recent US Energy Star ratings, so devices compliant with one set of rules should meet the other.