plugged in even when not in use, and consume from a few watts to 35 watts of power in that state. The report concluded that about 32 billion kilowatt-hours (kWh) per year, about 1% of total electrical energy consumption, could be saved in the United States by replacing all linear power supplies (average efficiency 40–50%) with advanced switching designs (efficiency 80–90%), by replacing older switching supplies (efficiencies of less than 70%) with advanced designs (efficiency of at least 80%), and by reducing standby consumption of supplies to not more than 1 watt. Since the report was published, SMPSs have indeed replaced linear supplies to a great extent, even in wall warts. The 2002 report estimated that 6% of electrical energy used in the U.S. "flows through" power supplies (not counting only the wall warts). The website where the report was published said in 2010 that despite the spread of SMPSs, "today's power supplies consume at least 2% of all U.S. electricity production. More efficient power supply designs could cut that usage in half". Since wasted electrical energy is released as heat, an inefficient power supply is hot to the touch, as is one that wastes power without an electrical load. This waste heat is itself a problem in warm weather, since it may require additional air conditioning to prevent overheating, and even to remove the unwanted heat from large supplies. Universal power adapters External power adapters can fail, and can become separated from the product they are intended to power. Consequently, there is a market for replacement adapters. The replacement must match input and output voltages, match or exceed current capability, and be fitted with a matching connector. Many electrical products are poorly labeled with information concerning the power supply they require, so it is prudent to record the specifications of the original power supply in advance, to ease replacement if the original is later lost. Careful labeling of power adapters can also reduce the likelihood of a mixup which could cause equipment damage. Some "universal" replacement power supplies allow output voltage and polarity to be switched to match a range of equipment. With the advent of switch-mode supplies, adapters which can work with any voltage from 110 VAC to 240 VAC became widely available; previously either 100–120 VAC or 200–240 VAC versions were used. Adapters which can also be used with motor vehicle and aircraft power (see EmPower) are