Don't put that RAM in your new system. It will really slow it down.
To find your PSU, open up the side of your case and look at the PSU. There should be a sticker on it that tells the wattage, the voltage on each of the rails (3.3V, 5V, 12V), etc. If you could take a picture of it and post it, it would be really helpful. However, I would assume that it is pretty weak, especially if it is from a premade computer like a dell, sony, hp, emachines, etc.
If you can spend a little over $500, I would suggest getting a new PSU.
this one has enough power for what I recommended