Tip- Dont Over Look the Power Supply
The power supply is often the most over looked part of a computer upgrade or build. This is not a part that should be left as an after thought. Not only does the power supply provide the power but in most cases it does 90% of the cooling and sometimes a 100% of the failing. I know that for the most part Im preaching to the choir but for people just doing upgrades for the first time or even their first computer build the power supply is often an unknown.
The ideas that the PSU provides different voltages on different rails, that the computer power supply is switched and must be under load to operate correctly, are important concepts that need to be understood by both upgraders and PC builders. Amperage and voltage levels on those rails needs to be at correct levels for that particular computer and its components. Just as the correct type of connectors and enough connectors need to be present to hook it all up.
Newer more up scaled power supplies come with more features that require more understanding to allow PC builders to take advantage of the new features. PC builders also need to understand why the best fit PSU is in the computer builders best interest.
People planning upgrades need to understand that the new components in most instances need more power and the old PSU may not be able to do the job due to limited output and wear and tear. To get that new component to work correctly you may need to replace the old PSU with a newer larger PSU or risk damaging the computer you are trying to upgrade.
The following links have helped me and maybe they can shed some light and aide to the first time upgrader and first time PC builder.