EmPower is a 15 volt DC connector type found on many commercial airlines designed to provide power to travelers' electronic devices. The system is limited to 75 watts. The use of a special connector is to prevent laptops charging at altitude and ensure that only approved adapters can be used.Some airlines offer it only in business class or only in certain types of aircraft or flights. Travelers can buy EmPower adapters, frequently from duty-free shops at airports, that allow them to run laptops and other electronic equipment without using battery power.Supporting airlines include:Adapters exist to connect EmPower plugs to cigarette lighter receptacles and most EmPower power adapters come with these.EmPower is a trademark registered initially by Primex Technologies (VA) and assigned to Astronics advanced electronic systems, Inc in Kirkland, Washington, USA. Subsequently, the trademark has been expanded to include not just the proprietary DC 15 V connector but also the AC 120 V 60 Hz in-seat power (and video entertainment) systems. American Airlines uses EmPower 120 V AC outlets (standard 2 prong plus ground) on their newer 737s.Many laptops will not function properly at 75 W. The new[when?] AC 60 Hz EmPower system provides more power than the DC system.The AC EmPower system converts aircraft AC 400 Hz or wild frequency power to standard AC 60 Hz to prevent additional stresses in laptop chargers already stressed by reduced cooling at altitude. Note that laptops on this system will still charge batteries. Modern laptop batteries, however include a temperature sensor that should compensate for the reduced cooling at altitude. This new system accepts various national power plugs and most laptop chargers will function properly at AC 110 V 60 Hz even if sold in AC 230 V 50 Hz markets.Apple offered an EmPower Magsafe power adapter for their MacBook, MacBook Pro, and MacBook Air lines of notebooks, and also includes a cigarette lighter socket adapter. However, this system only runs the computer and will not charge the computer's battery, and Apple indicates that users should not plug this device into a car's cigarette lighter outlet. This product has since been discontinued.Even though EmPower adapters are rated at 15 volts instead of 12 volts like cigar lighter receptacles, most accessories made for the so-called "12-volt outlets" have enough voltage tolerance to allow for a voltage as high as 15 without stepping down on a DC-to-DC converter.