MTBF and Life Cycle are both indicators of reliability. MEAN WELL uses MIL-HDBK-217F as the core of MTBF. An expected reliability is forecasted through accounting component number (exclude fans). The exact meaning of MTBF is after continuously using of power supply in a certain time, the probability of operating properly is 36.8%(e-1=0.368). If power supply is continuously used at double the MTBF time, the probability of operating properly becomes 13.5%(e-2=0.135). Life Cycle is found through using the temperature rise of electrolytic capacitor to estimate the approximate life of power supply. For example, SP-750-12 MTBF=769.3K hours; electrolytic capacitor C108 Life Cycle=202.2K hours (Ta=45� C).