Looking for correct power supply for Dell case switch


Apr 18, 2011
I currently have a Dell Optiplex 380 Desktop model computer being used as a secondary on my desk. I have a ATI Firepro V4800 I would like to start using to get back into Mechanical engineering but it is a full height card. A friend gave me the Mini tower from a Dell Optiplex 755 that would allow me to use the card as well as add some storage Drives. I checked and all of the components such as CPU Motherboard and drives will fit in the mini-tower case.

My problem is that I need a power supply that will work for this system as the one from the desktop model does not fit correctly. I tried the power supply that was in the 755 tower to begin with and it will not work. I think this is because the 380 is an i5 cpu and the 755 was a dual core.

Can I just order a good 300-400watt PS and be good to go or is their a certain type I should be looking for?
If additional information is needed please let me know.