Hi. This is my computer that i built two years ago.
x2 3800
2gb ddr 400
sata II 300gb
40gb ide
samsung sata burner
2 ide burner
asus a8nvm-csm
ultra vseries 500w
radeon x300 (got for free).

The problem is DMC4 requires 3.0 pixel shader, so I have to get a new one. I want to get the 4850 which requires 450W, and I have 500W, but my 12V rail is only 28amps and the psu only has one 4 pin pci express cable. I can get a 4 to 6 pin connector, but the idea of using a connector doesn't sound very safe. Do I need to get a new psu? Thank you for your time.

Your problem will not be your psu. The cpu is a major bottleneck, you cant use that card to its full extend with that cpu.

As dasjap says, that card will be bottlenecked by your CPU. Will you care? Considering the screaming performance you'll still get out of it compared to your x300, probably not. If you don't feel inclined to build a new rig any time soon, this may work out nicely. If you think you might build again before too long, maybe get something like a 3850 for this box (<$100 now), and then look at a 4870 or whatever else is available when you do a new build.

Bingo! You have a certified ATI power supply.

ATI Radeon HD 4850 System Requirements

450 Watt or greater power supply with 75 Watt 6-pin PCI Express® power connector recommended (550 Watt and two 6-pin connectors for ATI CrossFireX™ technology in dual mode)
Certified power supplies are recommended. Refer to http://ati.amd.com/certifiedPSU for a list of Certified products.

Thank you dasjap and jtt283 for your replies. Just one more question. I tend to build a new computer every 5 years. I want to play DMC4 at max settings, but I also do not want to be ripped off by price drops (260 & 9800gtx). Should I get the 8800gt or 3850?

I'm not familiar with "DMC4", but one of those cards would be more balanced with your CPU (CPU may still be the bottleneck, which is ok). Whichever you decide to get, choose one with 512MB of GDDR3 RAM rather than 256MB.

Thank you. DMC4 is Devil May Cry 4.

Yes u can run 4850. but ud prolly wanna pick up a better athlon FX for like 100 bucks

y dont u get a 4850 and then when u decide to build ur new rig....u could just use that instead of geting a new 1. 4850 would be better for future proofing than 8800GT

Why do you have 3 burners?

I would take the gt, because if you waite 3 years before updating again the 4850 would be out of date then. So save the money, there are quite a hugh differece in price between 8800gt and 4850

First, thank you for replying. Here is what I'm thinking, I'm going to get a video card to play DMC4 first. Then when I build a new system in 3 years, I can just buy the same video card and either crossfire or sli them. So in terms of sli or crossfire for the best price and future proofing, would 8800gt be better or 4850? To Doltron, I run applications like nero on one, decrypter on the next, and watch movies on the last.

Those wattage draw numbers don't match these at X-bit labs. They are showing a 109.9W max draw, or 9.1A.

X-bit labs - ATI Radeon HD 4800 Graphics Architecture: Long Anticipated Revenge? (page 14)

I can't find any in depth reviews, but I'm pretty sure, based on what I have seen, the ultra vseries 500w is suspect.

I would get a better single rail PSU.

Tom's hardware shows the 48XX drawing 250-275w fully loaded.

http://www.tomshardware.com/review [...] 64-15.html

You missed this

I usually play in a sitting for 3 hours or so. If I can run it at max settings, I will, if not I just run at average settings. So for the 4850, do I need to replace the heat sink and fan? What if I leave the case's side the video card is on open? Thank you.

No, you do not need to alter your CPU's cooling because of your GPU, but you do want to make sure your case has decent airflow through it to exhaust the GPU's heat.
Also, I re-read your OP, and you mention a "4-pin" PCI-e connector. There's no such thing. That connector has six pins. Your main mobo power connector uses 24 pins, likely provided by your PSU in the form of a 20-pin plug and a smaller 4-pin plug that attaches right beside it. Your mobo also has a 4-pin CPU power connector located behind the keyboard and mouse connectors. If this is your PSU: http://www.ultraproducts.com/produ [...] ductID=369, it has the 6-pin PCI-E power connector you will need.