Are shielded power cables necessary for

A power cable is a power cable. Think of it this way...You are not going to be sending any different type of current to the pc. IE. 110v

Now you do bring up another issue with the shielding though. Having a highly shielded cable is good in situations like when your network cable is wrapped around the power cable. Doesn't matter how neat you are when you put the pc in somehow all the cables get all tangled up and having a power cable that is projecting some electrical pulses around it canbe bad for the 1's and 0's going accross a network cable.

Hope that helps
Rad

Modern Power Supplies are designed to Trap/Filter power line variances, which would also include any airborne Radio Frequency hash. Under normal operating conditions I can see no need for the shielding of power cords.

Although Rad is right saying don't wrap your Cat around it :)

I try to avoid using the cheapest power cords.
If you have a large monitor, or a large power supply, the 18 Gauge wires in the cheap cords are not enough.

I use 16 gauge cords for most situations.

As to insulation and grade, that varies by the environment.

In a hospital, you need specific grades of insulation for cleanliness.
In an industrial environement, you need to assure that the insulation will not degrade in the chemicals that are present.

As to sheilding. That is also installation dependant.
For the highest security, you want to sheild the power cord to reduce the amount of signal available for a spy receiver to catch.

Chas