The only thing I have done inside the case is remove and replace
the system cards as well as add memory modules.
You should be fine. The PS isn't any more difficult. As previously stated
you may want to note how the cables are routed now and route them that way
again, just to speed up the process. Just try not to get them too tangled,
don't block fans, airflow, or vents and keep them off heatsinks. Its mostly
just common sense.
To make sure the screw holes match up you can measure yours and check the
spec sheets at the manufacturer sites. I'm talking about spacing and
pattern and not so much screw size. Screw type and size should be the same.
Look for a mechanical drawing of the candidate PS's. This might be overkill
but this will ensure that if Dell did something non-standard you won't get
bit. Also measure the physical size of your power supply for an idea if the
new one will fit in your case.
I have noticed that all the power supplies have an on/off switch in
the back. How does this work when there is an on/off switch in the
front of the computer?
The switch in the back, on the power supply itself, switches AC power to
the supply itself. If this switch is 'OFF', then your PC cannot be turned
on. If the PS switch is 'ON' then the PC, using the front panel switch and
power-management software/firmware, control what happens. The switch on the
front of the PC is monitored by circiuts on the motherboard. These
circuits, along with power management software/firmware control turn-on,
standy-by, turn-off, and possibly other functions of your PC. Check out the
Power Management applet in Control Panel for an idea of what I am babbling
about. Yes, this does mean that if the PS is plugged in and the PS switch
is on that part of the motherboard is receiving power. There is a '5volt
standby supply', +5vstby or something like that, to provide this power to
the motherboard.
Here is the current system configuration:
Dell Dimension 8300
250W power supply (unsure of the model)
Planar G0728 motherboard (according to configuration page at dell.com)
512MB memory
P4 2.6G
Check the video card manufacturer site to determine the new video cards'
power requirements. Video card manufacturers frequently recommend a minimum
PS power rating for their newer cards.
For long term upgradability look for a supply with a separate 4-pin
connector for the CPU. Just in case you upgrade your motherboard later.
Newer motherboards use these 4-pin connectors. Adaptors are available so
its not absolutely necessary. Also possibly look for a supply with power
connectors for SATA if you think SATA hard drives are in your future.
Lastly look for lots of 12volt amps. I have seen recommendations for a
minimum of 20Amps (20A) on the 12volt supply. This is because newer
motherboards power the CPU from the 12v supply. Video cards may also do
this, I am not sure.
good Luck