Replacing Power supply?

First off - my system: Gateway 700X.
3.0GHZ 800MHz FSB P4 HYPER-THREADING PROCESSOR,
Memory: 1024MB Memory Module, 160GB SATA Hard Drive, 18 LCD Flat Panel
Display Digital (18.1 viewable), 128MB NVIDIA GEFORCE4 TI4200 Graphics
Card, DVD-RAM/-R/-RW/CDRW Recorder, TDK CD-RW: 52/24/48,
SB Audigy2 ZS w/front panel, Boston Acoustics BA7900 5.1 Speakers (5 +
Boombox), Multifunction PS2 Keyboard, Logitec USB Optical Mouse,
Panasonic 3.5 Floppy ID Drive, Zip Drive, 120Gig External Hard Drive USB
(uses own power converter, Joystick - Cyborg EVO, USB, Microtech E6
Scanner (SCSI) and a Canon BJC-610 printer.

Current power supply is Model# NPS-250H8 A, pretty
sure its an ATX, no screws just catches.

I'm adding another SATA HD (200Gig, 7200RPM) and an
updated Graphics card (havent decided on model yet).

I'm looking at a range of 400/450 power supply for upgrade.
I've just been looking over some of the better known power
supplies and some of the terminology is unknown to me
(which makes it even more confusing to choose one to buy).
The pin-outs especially are confusing.

The question is: How do i know if the one i buy (on-line) will
have enough power connectors of the right type for my system?

The actual replacement seems fairly straight-forward, disconnect
the power leads and remove the present one, then install, connect
the power leads for the new one. Any problems to be expected here?

thanks,
savagcl

 

Thanks, PeteC, recon i'll do that.
CDW is my favorite on-line shopping place.
Think i'll call them on monday.

savagcl