I bought a Dell XPS 8100 back in October and the stock PSU was a 350W Delta one.
The Video card it came with was an ATI 5450 but then I changed it into a HIS 5770.
So my question is, will the power supply be able to run it because the minimum requirements are 450W with a recommended 600W PSU.
I already know it can run and its been running fine but a friend said its not good to use that weak PSU because it might fry my GPU or mobo or something.
The 5770 needs, at most, 6 - 8 amps. Your PSU is rated with a 25 amp 12 volt output.
As long as your PSU does not get too hot, you should be OK.
I have an OC'd Q9550 with a GTX260, a card requiring about 50% more power than a 5770, 4 GB RAM, three hard drives, and a sound card. Loaded with 3 instances of Prime95 and 3DMark06, it pulls about 300 watts from the PSU.
It depends mostly on the total amps the unit can supply on the 12 volt rails. Total wattage output of a PSU means very little actually for selecting a video card, it is only a general guide and takes into consideration there are a lot of cheap made power skimping units on the market.
If you have a couple of drives, a couple of USB connections, you are fine. If you have 5 drives, and 6 USB devices hooked up, you may start getting into trouble. Like said, manufactures overstate PSU requirements to ensure that they cover most all users needs, and quality of PSU'S on the market when suggesting or recommending. What is most important is the amp supply on the 12 volt rails, NOT the total wattage of a PSU. Dell in fact DOES use pretty good quality PSU's in their units, and your PSU though it does not have a huge power rating as far as total watts, has the power you need where it counts by suppling plenty of juice on the 12 volt rails.
In short, you are just fine.
(1) As JSC indicated, your total power consumption should be slightly under 300 Watts. My I5-750 @ 3.2 GHs w/5770, one SSD, two HDDs, a Blu-ray writer, and a DVDRW drive Running furmark, or Prime 95 draw about 300 Watts. Max load running a game should be somewhate less. At 300 Watts that would equate to 85 % load on the PSU, BUT that is only when stress testing (about 75%-80% when gaming), just surfing the web, playing a DVD, or running typical applications such as word, your power consumption is only around 125 Watts. SO unless you are playing games for 6 hours/day. Your OK, although for 50 Bucks, I'd be tempted to swap the PSU out for 400/450 watt corsair PSU to cover gaming..
(2) Concur with Dadiggle, Don't sweat the USB devices. (a) they are on the 5 V rail, not 12 V rail so0 only factor into total, and they ONLY add 2.5 Watts per port (not Device), ie if you have a USB hub and connect 1 device, or 4 devices the max is still 2.5 Watts at the computer. If the devices on the hub exceed that you must use a powered hub. On the 12 volt rail HDDs and DVD drives will only add a max of about 10 Watts.