New Power Supply

2 things:
While you're replacing your power supply, look for one with a larger down-facing fan. These ones run slower so are much quieter. They replace the same way and also help cool internal components more.

The other point is knowing what wattage you need.
http://www.journeysystems.com/?powercalc
Has a handy online calculator to give you an idea. All those extra USB devices will also tap your power supply. Just add a little headroom

I've had many power supply fans fail, but never an actual power supply. I just replace the fan. I have a half dozen or so generic ones at work here for that purpose. Generally the leads for the new fan don't work with the old fan so a little splicing is necessary, but no big deal. One big thing to remember when dissecting a power supply is that the capacitors can be hot (have power) for a day or so after removing power. It's not as bad as TVs, but I respect them anyway.

Also I've left power supplies open (without any cover) for extended periods looking for a replacement fan. This seems to provide adequate ventilation, but don't go sticking your fingers in there and watch your cat.

When you are plugging in the new power supply, take care to get the plugs in the right places and right way round.
I managed to connect the floppy drive connector wrong somehow and set fire to the insulation when I switched on! Fortunately it over-heated so fast (seconds) I caught it before too much damage was done.

The power supplies in PC offline switching power supplies. That means that the voltage exposed with the cover off can be as hundreds of volts. In addition, the cover is probably considered a safety enclosure which is designed to contain any burning pieces if the power supply fails.

As the power output capability of the power supply goes up, it becomes important to consider purchasing one with power factor correction. Power factor correction assures that the voltage and the current drawn from the power line is in phase. If your computer seems to be running hot, consider purchasing one that is certified to be a minium of 80% efficient.

Make sure that where you have located your computer has sufficient ventilation. I have replaced one computers power supply and 6 months later the owner had the power supply fail again. I was surprised at that and asked some questions about their setup. It turned out that the computer was enclosed such that cool air couldn't get in. For every 10 degrees C a capacitor temperature is increased, its life is cut in half.

Speaking of capacitors, there is a specification that you usually don't see on most PC power supplies and that is hold up time. Hold up time is the amount of time the power supply can deliver its load with no input power. Usually you would like to see this number be longer than one line cycle (1/60 Hz = 16.7 milliseconds). This helps keep your computer from crashing if there is a power flicker.

You should examine the output voltages and currents on your origional power supply and make sure that the new power supply has a current rating for each voltage at least as high as the origional one.

Make sure that the connectors on the new power supply match the original. Not all power supplies have connectors for the newer serial ATA harddrives.

As far as fans go, make sure that your case does not block the vents or fans on the power supply.

As far as the twist tie is concerned, it is possible that a twist tie used to bundle the power cable or the output cable found its way into the power supply. If it did, the high voltage and current available inside the power supply could easily have shorted out to the case.

Make sure that your wall outlet has a good ground. There is a short to the case, you want to know that the current has some place to go other than through the next person to touch the computer. Don't use a cheater plug, all three wires are required.

This is probably more than anyone wants to know.

What about problems with power supplies for CRT displays?

This article is pretty good but omits at least two items that are important in my opinion:

1. WARNING: Some (in my opinion nefarious) computer vendors, notably Dell, make a few changes in the pinout (which functions connect to which pins or contacts) of their power supply (and of course the matching connector on their motherboards) with the worst possible result: You buy a standard ATX power supply (with either the 20- or 24-pin motherboard ATX power connector options) and you find that it physically mounts fine (# 2 below) and all the connectors match so you hook everything up and when you apply power, you generate smoke in either the power supply or your computer (motherboard, drives, peripherals, everything) or both. I don't know if currently shipping Dell computers still do this, but many already out there do, and those are the ones most likely to be considered soon for power supply replacement.

Conclusion: If you have a Dell computer, you MUST somehow reliably figure out if it requires a Dell power supply or a standard one (my experience with Dell Tech Support is don't bother; they won't actually help you). This may also apply to other brands, but I am not aware of any.

2. If buying a replacement power supply in a physical store, take along the old one or otherwise assure yourself that the new one will mount in the same space (including screw-hole locations) and that the leads (wires) and connectors will reach all the necessary connections. If ordering online, find a computer geek to help you (or perhaps call and ask the vendor) to achieve the same goal before ordering.

The noise maybe not the power supply. It could be the fan on the video card if that computer has one. Of course one would verifiy it before replacing the power supply. Be carefull when buying power supplies. You get what you pay for. The cheaper ones have lower/size gauge wires.

Hiya is it worth replacing power supplies on laptops yourself as well?

EDITOR'S NOTE: I've never done so. Everything is packed so tightly inside the laptop case, so it might require removing and replacing quite a few parts to get the job done.

Here's a strange one: My computer only shuts down when it tries to read a CD (any CD) I've inserted into the CD-RW drive. I hear a "click" and it just turns off. Is the problem something with the CD-RW drive, or with the power supply? Or both?

EDITOR'S NOTE: My guess is that the CD drive is bad. But before you replace it, try replacing the software driver. Check the CD manufacturer's website and see if you download the driver.

I replaced my power supply. I have been using it for a month now. Is it normal that there is burn smell coming out from the power supply? Is it because it is new? Will the smell go away after some time?

EDITOR'S NOTE: I don't think that's a good thing... especially after a month's time. Usually that burning smell indicates that there is a problem.