|Please, lets get the terminology straight!!!|
You computer's case is NOT your CPU. Your CPU is one component inside of your computer's case and is probably made by either Intel or AMD.
NOW on to the problem. I generally do not recommend using the power supply's manual power switch to turn off your computer, even if you wait for the system to shut off properly first. The manual rocker switch on the power supply is at best a 50 cent part (US) and apparently does not stand up to continuous use. If you are uncomfortable with the power in your town and prefer a manual power break, use a surge protecting power strip and turn that off instead. This way if the switch on it goes, you can replace the power strip or possibly replace its switch. Power supplies are not designed to be consumer serviceable and can contain power stored in them that can prove to be dangerous. Finally, being that you refer to the power supply as "SMPS" I infer that you are from India and know that India is known to have an overabundance of poor quality power supplies.
Replace the power supply but purchase a quality unit by a name brand like Corsair, XFX, OCZ, and a few others. For specific models to look for, look on Newegg.com, and filter with the following details: Single 12Volt Rail, Active PFC, 80% or greater certified efficiency, and look for a wattage rating the same or slightly higher than your original power supply.
This is a good economy model: http://www.newegg.com/Product/Produ...
You have to be a little bit crazy to keep you from going insane.