got a new computer now that replaces the old one that blew up, already want a better video card though as its the only thing letting the system down really.

it came with an ati x1300pro and i fancy an x1950pro or x1950xt but they recommend a 450w PSU and we only have a 305w, the thing is they set this requirement assuming a fully loaded system where as we are running 1xHDD, 1xoptical drive and thats about it really as everything else is on board so its not like we are pushing the limits as it is.

i think it will be fine myself, anyone out there with any experience with this?

OOps, I didn't know you had to have an upgraded power supply if you were upgrading bits in your PC.

I got a new tower from Evesham on Monday and straight away glued my old 400G seagate HDD and my old philips DVD writer in there, along with the standard DVD and HDD that came with the tower.

How should I check if I've got enough power to cope? Who makes the rules?

i think the PSU makers have sided with the gfx card makers to confuse people into buying more stuff myself.

Bear in mind that 305w will be peak not constant, plus that may not actually be what it puts out. I would have to say I would recommend a bigger power supply.

looking around at power figures this is what i have found as an estimate:-

core2duo - 65w

dvd rw - 25w

HDD - 25w

2x1024gb - 15w

usb device- 5w(x6)

so surrently looking at about 160w + video card and the video card i'm looking at is around 100w so *should* be fine??

You got any figures on howmany amps through each line on your PSU just because your total peak wattage is more than average power consumption doesnt mean your PSU will be able to cope with even normal demands your 305 watts is spread across all the lines, Do you know how many 12volt rails you have? If you are drawing more power through one line than the PSU is designed about you could well exceed ratings on the wires themselves and end up heating things up.

Remember that the stability of the power provided by your PSU is crticial to system stability, the more fluctuation you get on your power lines the more crashes you are going to get, also the closer to the limit you push your PSU the shorter life span it will have.

Your PSU MAY provide 305 watts maximum peak power but thats 305 watts for a short burst across 3 voltage lines your 12volt line MAY only have 100 watts peak power and 65 watts reliably!!

Found a 300watt power supply laying around here the 12 volt rail is rated at 10 amps, thats 120 watts peak before it blows "safe" draw on the 12 volt line would be closer to 80 watts or 6 amps....

The closer to the limit you draw the more likelly reliability problems or component failures.

ATI dont make much money from the sale of PSU's, I would suggest their guidelines are based on a realistic safety margin based on what they know about their cards power draw across all voltages and PSU's abilities to supply to each voltage.

I wouldnt suggest ignoring the manufacturers stated requirements assuming a huge safety margin and then proceeding to run right to the limit. Its just not good practice in my opinion. A good PSU is an investment in not losing work and less frustration its also a very much overlooked factor in PC crashes.

also worth noting some of that 305 watts peak will be on the - lines, and that wont be helping you much. probably as much as 20 watts of stated power not helping.

Bengie, you forgot the memory chip consumption, plus all the other components on the motherboard, onboard sound and lan all take as much power as they would on separate cards.

My HTPC has a 300W power supply, currently running 4x512MB memory, 1xDVDRW, 2xHD 1xTV Tuner,1x soundcard, 1xnetwork card and the geforce 7600 graphics card and its struggles somewhat. Plugging a powered USB device in the front for more than a few mins is enough to overload it and hang the pc.

looking at a decent 500w+ PSU already

Tagan supplies usually deliver a the amount they say on the side as a constant deliverable not a peak unlike some cheaper supplies.

Just don't get caught out by some of the knock off ones with similar names to other quality supplies

I've found antec very good, quiet and always good reviews.

Yep I would rate the premium antec PSU's also

Best advice I have is make sure you do get a decent branded PSU, and not a cheapie that offers a zillion watts!

I'm currently using an Antec, a Seasonic, and a Silverstone PSU, in various machines, and they're all coping nicely with the 100's of devices I have attached to them.

Here's a link to a power supply calculator: eXtreme Power Supply Calculator - What Power Supply Do I Need

May give you a rough idea as to how much power your pc actually needs.

Antec, Hyper, Tagan, or (as simonsheil recently obtained) a Nexus - 550watts, and virtually silent.

Or Enermax...

Ive got a 600w Enermax liberty... its great

As above.. it always pays to get a decent brand PSU.. ive had a "cheap" psu go on me before.. and it took the mobo, cpu, mem and a hdd with it :(

Dont rate Hyper myself, of course the one I had might have been a rogue unit, but it gave reliability issues and died ata bout 14months :(. Antec I have used extensively in the past and would rate them for long term reliabilty and low noise. They tend to give good solid power. Tagan Seasonic and Enermax all get good reviews from the enthusiasts I would be happy to buy any of those brands.

The main thing to be aware off besides the 'rated' power is:

* Continuous power should be at least 20=30% higher than the actual continuous load

* Power figures given tend to be for max power for the headline figure. This figure is frankly useless

* Good quality PSUs can usually take a load well, 'el cheapo' ones can work well but you'd be well of spending a few quid more :P

* Temperature - most PSUs, Enermax and other 'branded' ones included, are rated at a temp of 20 degrees C or 25 degrees C. Inside a PC case and/or a warm room during the summer, those temperatures are just crazy. It will get up to around 38-45 degrees C unless you have aircon. At that point, ratings are WAY lower. Thus having reserve makes a lot of sense

* If you PSU dies, it tends to kill a lot of stuff if this happens in a bad way. With branded gear chances are there is more intelligent protection built in for that event. A cheap PSU wont have anything like it and just fry your expensive mobo, cpu, ram etc. This is from bitter experience unfortunately :(

I bought a graphics card power supply that fits in a 3.5 inch bay and powers up to two graphics cards

doesnt fit my mobo though which is a nuisence, I'm sure i'll use it at some point though.

thermaltake graphics psu - Froogle