I have a Dell 4550, P4 2.4 with a 250W PSU. I have access to other Dell PSUs. How can I tell if they will fit/work? I have no way to measure them. Here's the model # of what I have: PS-5251-2D Here's what I'm looking at: NPS-330CB L, Used in : Poweredge 400SC and Precision 360 NPS-350CB, Used in : Precision 370, Dimension 8400 NPS-305AB C, Used in : Dimension 4700, 8400, Poweredge 400SC and Precision 370 Thanks for the help!