How do i know when i should change the power supply?

I dont want it to just cut out one day and ruin my system.How do i know when i should change the power supply?
That's hard to say. it depends on the quality of the power supply you have, and at what percentage of it's maximum potential is actually being used for prolong periods of time. You want a 20% buffer between th power you are actually using and the maximum power your power supply provides (in watts). For example, a good power supply, made by a reputable manufacturer using quality components is going to outlast, and provide more stable power over time than a cheaper power supply. Also, a power supply that is always using 90% of it's maximum wattage, is going to burn out a lot quicker than a power supply that uses only 75%. For example, lets say we have 2 identical power supplies, both rated at 300 Watts. PSU 1 is always running at 290watts, while PSU 2 is powering a system that maxes it's power load at 255watts. PSU 1 will fail first, and run hotter.How do i know when i should change the power supply?
when the one you are using is about to run out.How do i know when i should change the power supply?
There is no definative answer to that question, I have some computers that the power supply has lasted 10 years others only lasted 3 if you are paranoid about it failing then replace it every 2 years or so. But it is really a waste of money to do so a good quality power supply will last as long as the computer is useful.How do i know when i should change the power supply?
The best way to tell if your PSU is working correctly is to make sure it's got stable voltages using a multimeter.



I'll try to explain as best I can:



Step 1: Unplug the PSU completely from the wall and remove it from your computer.



Step 2: Make sure the voltage selector on the back is in the correct position.



Step 3: Now you're going to have to power on the PSU while it's outside of the computer. Plug it into the wall and short out the GREEN (14) wire with one of the BLACK (13%26amp;15) wires right next to it. A simple bent paperclip will do. Please see the image for reference:

http://forums.tweaktown.com/attachments/



Step 4: Now that you have the PSU powered on, you need to make sure the internal fan(s) are running.



Step 5: Now with your multimeter check pin 9, it should be a PURPLE wire with 5v.



Step 6: Now test a YELLOW wire and make sure it reads 12v.



Step 7: If all the voltages check out OK you're good to go, it's a good PSU.



If any voltages are off by more than 1v you should buy a new PSU and recycle your current one or perhaps you're too lazy, and don't want to check your PSU for problems? Well it's better to buy a new quality PSU and be safe than to find out the hard way that your PSU is dying.



Here's a great place to order a new PSU if you decide you need one. I can personally recommend this online store because I purchase all of my computer parts from them and have never had a problem:

http://www.newegg.com/Store/SubCategory.