A: Since you don't say what's already in your system, I can't estimate your current power requirements-but maybe you can. I use the 150+12 rule when calculating power demands in a PC.  The initial 150 watts (W) covers the motherboard, CPU, and memory; then I add 12W for every drive and @sion card.  For example, if your system had a floppy drive, a hard drive, an internal CD-ROM drive, a video board, and a modem, I'd calculate the power requirements to be about 150+12+12+12+12+ 12, or 210W.  This is well within the capacity of a 22OW power supply.  Doift worry about external devices; they have their own sources of AC.  Survey your system and calculate the power yourself.  Now compare that to the power capacity listed on your power supply.  I bet the number' will be very close.

Since the 150+12 rule provides for a bit of coverage, you cotdd probably add a drive and/or expansion board without upgrading the power supply.  But your plan adds two drives d an MPEG-2 decoder board (required for the DVDROM drive).  YoLfll need an extra 36W or so (12+12+12) to support the new devices .  Add 36W to your original calculation, and you may find that it exceeds the power supply's ratings.  This means you pmbably should upgrade the power supply to a model thafs equal to or larger than the power demands you just calculated.  In this example, yotfd need about a 25OW (210W+36W) power supply.

It doesn't hurt to use a power supply with a higher capacity.  You may not use all of its capabilities now, but if you have plans to expand even further in the future, the investment in a 30OW supply may someday come in handy.
 
 

                                                            SOURCE:  Zdnet and Computer Currents