Graphic card and power supply.....?

Depends on what the TDP of the video card actually is. Video card manufacturers often grossly overstate power requirements. This is done because there are alot of cheap no/off brand PSU's that don't produce the amount of power they are rated for. For example in my work PC has a Radeon 6570 video card it in. The manufacturer says that it requires a 400 watt PSU. But I know that in reality, the TDP (the amount of power the card will draw at stock speeds) is only 44 watts. And that I'll easily be able to power the card with my work PC's stock 240 watt PSU. And sure enough my Work PC powers the card flawlessly. If you mentioned what video card you have, I could tell for you sure whether or not you're cutting it close on the power requirements.

Also no discrete card currently available draws 400 watts of power by itself. The stated power requirements from the manufacturer take into account all the power requirements of the PC as a whole. So if you have a card that requires a 400 watt PSU, you don't have to add another 200 watts or whatever onto that to taken into account the CPU/mobo/RAM/HDD, etc., it's already been accounted for, and this is another reason why power requirements are often overstated, they have to take into account that someone might have a highly loaded rig with like 4 HDDs, and fans galore.

If your PC is running fine with video card in it, you're probably fine on the power consumption front. If your PSU couldn't keep up, you'd know it, as your PC would shut down under load.

It's weird if your PC is running fine with 300W PSU while your card requires at least 400W. It usually won't work at all. I've tried that myself.

If you're asking what the relation is, it's that anything you connect to the motherboard draws out power from the power supply, so if there's not enough power it will cause power failure which will cause your whole system to shut down and not able to start until there's a sufficient power supply available.

So yea, if you want a card that requires at least 400W, you get AT LEAST 450W, and the more the better and safer of course.

ye it can handle it. But you should have put the information of the mother board as well to see if the motherboard is compatiable with your card. But with 2 fans to prevent over heating, it's good. And the card needs 300watts of power supply so your ready to install it.

Oh my.... I have never thought of that but nah. Gotta get more than 650w. I do not know how much power CPU take up but perhaps at least 125w. Newegg.com is selling a high end seasonic x750w with 80 plus gold for $99.

no no no

If your graphics card requires at least 400Watts then your power supply should be at least 600Watts.You add additional 200Watt which includes power for other components + the power supply gets warned out over time so for example after 2 years it actually becomes 550Watt instead of 600Watt(just an example).

Add 200...

it is generally not a good idea to run with minimum power. if at any point the computer requires more power than is available, it will short circuit and everything may get fried. it is better to have more access to power than you need than to not have enough power when you need it.