No issues using a big power supply. The rating is there to tell you what the max power the PSU can supply. If your system pulls 100W, that's all the PSU will provide. Theoretically, you can throw in a 1000+W power supply, but if you don't get near that level of power draw, you're sort of wasting your money buying such a big power supply. There's also some efficiency considerations when you have such a big power supply but only drawing a fraction of the power it can provide.

 

Thank you so much that was great help.

 

In modern PCs it's usually the graphics card that dictates how much power you need.