yes the card draws power from the 6 pin pci express power cable.

 

i thought dell didnt provide psu's??

what is it i need to look for in a replacement psu? obviously having the same connectors so in my case its sata power connectors for my hard drive and dvd drive, 24 pin motherboard connector and 4 pin power connector and finally pci-express connector.

 

my current unit is 12v so guess i need to get same voltage just higher watt.

You could call Dell Spare Parts(1-800-357-3355) and tell them that you need a power supply for a Dimension 8400(350 watts 28 amps), it will work in your E520.

Or get this one:

http://www.pcpower.com/products/viewproduct.php?show=S47ATX

It's the same as the model that is recommended, but has the switch and is $50 less expensive.

this is what i was thinking of using to replace the psu with:

 

http://www.coolergiant.co.uk/products/psu/liberty/ELT400AWT/index.asp

Sorry, I don't have a fix or recommendation for you, but a possible explanation.

 

Notice that when you first turn on a vacuum cleaner or air conditioner, the lights dim briefly?  Startup current can be 2-3 times operating current.  To determine if this is the case in your system, unplug power from both drives.  If it starts that way (just power--obviously won't boot), startup overload is the problem and a 350W supply should fix it. 

 

But if you'll forgive the engineer-speak, just between us the 305W supply should be able to sustain the startup transient, ramping voltage at a rate* that doesn't trigger overcurrent or ramping down the overcurrent threshold from 200% to 100% over the first 500ms.  What's overloading is the +12V rail, having to start the HDD motor from dead stop and charge the graphics board filters at the same time.  (* Voltage ramp rates are sometimes defined by Intel, how the supply designer achieves it is his/her challenge.)

so would you agree with contrvir that i should opt for the Dimension 8400's 350w psu as best fit for my E520?

 

i am based in uk and pcpower.com that every one in the forum rates so highly isnt much good to me to get a repacement.

 

will the 8400 psu have the connections i require, i need 2 SATA power connectors at least.

i have measured up the specs for that psu against my psu from my e520 and is exact same size and dimensions.

 

i know that this psu has a fan that would be located at the top of the case where there isnt a grill but other than this it is the same.

You've hit the bisquit on the crust, plipy.  Aftermarket supplies can be electrically and dimensionally (pun?) identical, but you have to contend with things like fan discharge direction, location of mounting holes, and wire length.  Can be daunting.

 

Rather than get stuck with something it turns out you can't use, I'd just buy the Dell supply and be done with it.