A 400 watt switching power inverter supply does not necessarily use more power than a 250 watt power supply. If you use each available slot on the motherboard or every available drive bay in your PC chassis, you may need more power. If the total power in the device is 250 watts, then using a 250 watt power supply is not a good idea because the power supply should not be loaded to 100% of its capacity.
According to PC Power & Cooling, Inc., some power consumption values ??(in watts) of common devices in personal computers are: Accelerated Graphics Port (AGP) card = 20 to 30 W
Peripheral Component Interconnect (PCI) Card = 5W
Small Computer System Interface (SCSI) PCI Card = 20 to 25W
Network interface card = 4W
50x CD-ROM drive = 10 to 25W
Every 128m RAM=10W
5200 rpm integrated drive electronics (IDE) hard drive = 5 to 11W
7200 rpm IDE hard drive = 5-15W
Motherboard (no CPU or RAM) = 20 to 30W
550 MHz Pentium III = 30 watts
733 MHz Pentium III = 23.5 watts
300 MHz Celeron = 18 watts
600 MHz Athlon = 45 watts
power inverter supplies with the same form factor (“shape factor” refers to the actual shape of the motherboard) are usually distinguished by the power and warranty period they provide.
POWER INVERTER 