Saw this as a printed article so I typed it up and figured that you all might find it usefull. If you have any different information, or updates or additions please post them below, I think that this could come in very handy to all involved!
How much power do you need? If you're running a micro-ATX motherboard with embedded graphics and audio, and a single 5400rpm drive, that wimpy 150W power supply might just do. But if your rig pushes half a gig of RAM, dual procs, Ultra2 SCSI RAID, and a GeForce 256, even a 300W supply may leave you bent.
We've compiled a list of roughtly how much power is consumed by common parts. By now you should know not to judge your power supply by overall wattage alone, so look at the demands on each separate line. Nonetheless, when looking at overall watage, add the requirements of every device in your rid, then multiple that number by 1.5 (because you should be taxing from 30% to 70% of your power supply's capacity). Some of your individual components may actually list their specific power requirements, so use those numbers for more accurate calculations. Always remember, if you need to figure out wattage, multiply the voltage by amps.
Also don't forget that LCDs and GPSs and even the keyboard (0.2-0.3W 5V) and mouse (0.1-0.2W 5V) take power, USB adapters too.Code:High-wattage AGP Card 20+W +3.3V Average PCI card 5W +3.3V Cached SCSI PCI controller 20-25W +3.3V Floppy Drive 1W +5V 10/100 NIC 4W +3.3V 50x ATAPI CD-ROM 10-15+W +5V & +12V 50x ATAPI CD-ROM 10-15+W +5V & +12V 8x4x32 SCSI CDRW 17W +5V & +12V SCSI CD-ROM 12W +5V & +12V RAM 10W/128MB +3.3V Ultra2 SCSI PcI Card 5W +3.3V 5400rpm IDE Hard Drive 5-11W +5V & +12V 7200rpm IDE Hard Drive 7-15W +5V & +12V 7200rpm SCSI Hard Drive 24W +5V & +12V 10000rpm SCSI Hard Drive 10-30+W +5V & +12V Motherboard 20W +3.3V & +5V 550MHz Pentium III 30W +3.3V 733MHz Pentium III 23.5W +3.3V 300MHz Celeron "A" 18W +3.3V 600MHz Athlon 45W +3.3V
IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.