I have a Dell 8250 with its original PSU at 250W and its original motherboard. If i upgrade the PSU to a 350W will that create any problems such as overpowering the motherboard or anything of that nature? I talked to a dell representative via chatroom and he said, I cannot b/c the motherboard will not handle it. Is this true? or can i indeed upgrade to the 350W and not do any damage to the system?
Your components will be fine.
Each component 'draws' power from the PSU, so for example your CPU will draw 75W from the PSU. So for a 250W PSU, you'll have 175W available for other components. It doesn't matter how much wattage your PSU has, as long as it can handle the power that all the components 'draw'.
The only thing I can think of is that the new PSU might not fit where the old PSU is. (Proprietary Dell case, what else?)
So you'll probably want to do some measuring before you go and buy a new one. Otherwise you might have to modify your case.