Geek Squad boy said to install a 350W ps into my emachines C2825. When I went to install, I found the original ps is only 250W. Do I need to go exchange for a 250W? or is it safe to use the 350W?

If you put a 350W Power supply in, it won't fry your computer. In fact, your better off with a 350W since you will have more power in reserve in case you need to add more optical drives or such.

The PSU's used in factory built PC's are just above the systems power requirements. You would be much better off with 350w even 300w. If you need an upgrade down the road you will not have any power issues.

The previous answer is correct, to add more detail let me say that when I have tried to use my 2 DVD drives, my 2 Hard disks, my Nvidia 6600 GT and my floppy drive (it needs power too) the system had difficulties delegating the power to all these devices. I had put a 350W one from Trust, it solved my problem for 6 months but now it is not working (for other reasons). Until I get the time to buy a new one I put back the old one. By disabling the floppy and one of my DVD drives I get by just fine for the moment.

35ow is batter you may be additional parts added it will be use.