Adding a new terabyte HDD... enough power?

I have a 250 watt Dell 530s (a slim desktop).

I want to add a new terabyte hard drive in my computer. The problem is I don't know how much watt I have left to spare. I posted this in another forum and one person recommended me to use a multimeter.

I have a Celeron 450 2.2ghz, GIGABYTE GV-R435OC-512I Radeon HD 4350 512MB 64-bit GDDR2 PCI Express 2.0 x16 (said to take up 35 watts), 320gb HDD SATA, DVD-RW, 2 x 1GB sticks DDR2.

Here's the original link. I'm not sure if they are paranoid or not. When I asked the same question for my graphics card, the person said I have more than enough power. The user wasn't worried.

Here's my original post:

http://www.computerforum.com/15793 [...] -what.html

Thank you.

Shouldn't be any issues

As Johnny said the gpu is more the issue, as hard drives take very little power. If you want you could just swap the drive instead of having two then you wouldn't be increasing the load.

FYI
The video card you have installed now recommends a 300W power supply.

It would be better, but then consumers would have to do addition on their own. If you've ever had to work with the public, then you already know what a bad idea that is.

That card uses about 50 watts and here is a link to show harddrive power requirement under load
http://www.tomshardware.com/charts [...] ,1026.html

edit to add
your cpu is 35watts

You're an engineer, aren't you? (Don't worry, I am too)

Honestly though, everyone's right. Modern HDDs consume a maximum of around 10-15W during startup (when the discs start spinning) and consume 5-8W during peak loads (constant access) at idle most are 3-5W and in sleep (powered on but discs not spinning) less than 1W. These are pretty generalized numbers, yes, but this gives you a scale for power consumption to compare to your CPU (35W) and GPU (50W). All-in-all you can see the power draw is pretty neglegible. If you're truly that concerned then buy a P3 Kill-A-Watt (~$20) and get the total power consumption of your system to ensure it doesn't get close to the max of the PSU.