Power Supply actually is composed by transformer and alter current /direct current the converters and steady voltage " last electric apparatus synthetically " that circuit make up not corresponding . This is " turned into the electric apparatus synthetically " Include two main parts inside - " transformer " and " current converter " ,And these two part itself have consumption of electric energy, the steady voltage circuit that they attach to is no exception naturally, so the power itself is a " power consumptive device " . Input energy of power can not 100% is turned into the effective energy available for every part in the CPU, the question of conversion efficiency has appeared like this. Conversion efficiency of the power = CPU real-time output power /input real-time power * 100% A, different power supply products, its conversion efficiency is different. B, the same power supply product, under different working state, its conversion efficiency changes too. A is very easy to be understood, because between different power products, their inherent varying voltage circuit, current converter and function circuit will all be different, it was not originally the same to combine with one's own power, so conversion efficiencies were different was natural. But why will conversion efficiency of the same product be changed? This will be talked about from voltage of output of the power firstly: Ex: Suppose the input voltage is specified 220V, but have such different output demands as +12V, +5V, +3.3V,etc. it show that power has three different kinds transformer at least (" Coil Convolve rated " , " EMF Leakage rated " Difference) , because this three kinds of transformer exhaust are the same, meaning that output +12V, +5V,and +3.3V’s power supply their each corresponding transformer conversion efficiency are not the same also. The machine at the different working state, frequency of utilization of every part and working load will be different, caused the working load at the outputting return circuit floated, so under different working state, the conversion efficiency of the power supply changes too. We know through the analysis above, the flows of power supply’s own consumption not too much, but output’s float getting heavy. Usually thinking as that output load more heavy, the power supply unit load share consumption more smaller, at this moment the conversion efficiency is more higher.