How to check whether a SMPS is in working condition?

SMPS stands for Switched mode Power Supply. It gives power to all the components in your computer system.

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/shorting a small wire between green color(PS_ON) and adjacent black color wire (COM). After connecting, plugin power cable and switch on the SMPS. If SMPS fan runs, SMPS is working.

There are many other problem too, if computer is dead, but please try this step first.

Calculation of UPS or Inverter Backup

Before calculating the Battery Backup, let us know a few factors that vary battery backup.

For UPS with 875VA we can us a maximum load of 640 watts and 677VA we can us a maximum load of 540 watts. The main thing we have understand is that what ever may be the UPS wattage the battery backup will not vary. The battery backup will only vary depending on the battery Ah and the Usage Load.

To calculate UPS backup, We have a simple formula:
                      UPS Backup = Battery Ah * (Volts/Load) * (1/Powerfactor)

Example: Let us calculate the backup for a system UPS

Load is the usage power, suppose we are running a PC then the load is around 300 watts
Power Factor varies for device to device, the average power factor is 1.4
Voltage is the voltage of the battery. For a single battery the voltage is 12v. If the batteries are connected in a series   Voltage = 12 * no. of batteries.
Battery Ah is the battery ampere used for the ups, System UPS battery AH is 7

                     Then   Battery Backup = 7 * (12/300) * (1/1.4)
                                                       = 7 * (0.04) * (0.7)
                                                       = 0.19 hours
                                                       = 19 Minutes

Note: You can use the same formula for calculating the battery backup for home UPS or an INVERTER.