1. SMPS

2. Trouble shooting
If your computer is dead and even not a single lights glow on your Motherboard, the basic need is to check is SMPS. To do so, remove power cable from SMPS and unplug all connections of peripherals (Hard disk, Motherboard, DVD etc). Now you can check SMPS easily by connecting a small wire between green color(PS_ON) and black color wire (COM) as shown in figure. After connecting, plugin power cable and switch on the SMPS. If SMPS fan runs, SMPS is working. - See more at:

3. Troubleshooting
. The first thing to check if your computer stopped working is its power supply. The main causes of PSU failure are overheating, voltage surges in the input line, and dried out electrolytic capacitors. All this may result in a catastrophic failure of one or more transistors or rectifiers. This in turn usually opens the input fuse (see this tutorial for block diagram and theory of operation). To check your unit, first of all you need to turn input power off and remove your PC cover. Then unplug all the cables coming out of the PSU. To enable a stand-alone PSU, you need to ground PS_ON# pin (see connection diagram to the left for the test setup). In an ATX-2-compliant model it means shorting out pins 15 and 16 on the 24-pin connector. You can do it by using a small piece of a copper wire. In an older 20-pin unit you need to short out pins 13 and 14. Note that some manufacturers, such as Apple, HP and Dell used proprietary non-standard connector sizes and pinouts: see more info here. After enabling the unit you can turn on the input power and check output voltages one at a time. To measure any voltage connect a voltmeter between a respective pin and any common. You can use an off the shelf tester to simplify this process. If you should decide to open up a PSU, always unplug it first and then wait at least five minutes to let all capacitors discharge. You should not do a troubleshooting unless you have a proper electronics training and know how to work with high voltage circuits.

4. ATX SMPS:
ATX stands for Advanced Technology eXtended. They had 20pin Power connector, this is called as ATX power connector. They were used in Pentium-III, Pentium-IV and AMD CPUs.

5. Types of smps SMPSs are three types. AT SMPS ATX SMPS BTX SMPS
AT stands for Advanced Technology. These are all old SMPSs. They had 12pin power connector, this is called as AT power connector. They were used in Pentium-I, Pentium-MMX, Pentium-II and Pentium-III CPUs.

6. BTX SMPS:
BTX stands for Balanced Technology eXtended. They have 24pin Power connector, this is also called as ATX power connector. It has 15pin SATA power connectors. They are used in Dual core, core2duo, Quad core, i3, i5, i7 and latest AMD CPUs.

7. precautions Use smps without earth pin?
While this won't affect the functionality of the power supply, it does compromise the safety of the unit, since a fault such as stray power or wiring failure can cause the case of the computer or power supply to become electrified, creating a risk of electric shock. The ground pin is intended to prevent electrical current from reaching external metal parts.
You can use the cord, but you shouldn't because it would not be very safe to do so.

8. Installation Space
When mounting two or more Power Supplies side by side, be sure to provide spacing between them as indicated in the table on the right or greater.
Cooling Method
The life of the Power Supply is determined by the life of the electrolytic capacitor that is used internally. The capacitor follows the Arrhenius law, i.e., the life is halved by every 10°C increase in temperature and double for every 10°C decrease in temperature. The life of the Power Supply can thus be extended by lowering the internal temperature of the Power Supply.

9. Methods for Lowering the Internal Temperature of the Power Supply
The internal temperature of the Power Supply becomes saturated when the heat generation equals the heat dissipation. If heat dissipation is too low, the internal temperature continues to rise, so dissipation must be considered when mounting the Power Supply. Use the Power Supply in an ambient temperature that is within the values specified by the derating curve.
Heat Dissipation for Natural Cooling
Provide sufficient ambient space for air convection and provide air holes. We recommend a metal plate as a mounting surface. Forced-air cooling is strongly recommended

10. Life Expectancy and Recommended Replacement Period
The life expectancies of OMRON Switch-mode Power Supplies are defined under the following conditions and are designed to be 8 or 10 years minimum.
Note:The life expectancy does not apply to the fan.
Rated input voltage
Load at 50%
Ambient operating temperature of 40ºC
Standard mounting conditions
The replacement period and life expectancy are reference values only and do not imply a warranty of any kind. Use them as guidelines in designs and applications.

11. Fan Life and Replacement
Some Switch-mode Power Supplies have built-in fans for forced air cooling. The fans in these Switch-mode Power Supplies also have limited lives in addition to the lives of the Power Supplies themselves. The fans must be replaced periodically. The replacement period for the fans varies with the Power Supply model. Refer to the datasheets for details.
Foreign Matter and Dust
There are slits in the Power Supplies that allow internally generated heat to escape to the exterior. Foreign matter or dust can enter through these slits, causing the output to be reduced or to stop. We recommend that you remove foreign matter and dust from around the Power Supply during periodic maintenance.