For the most part, power supplies are adaptable with each other, if you take the one you currently have to Best Buy or other electronics store, you shouldn't have a problem.
By the way... welcome to Techspot
Thanks. What do you mean by adaptable to each other exactly? My plan was to buy a new power supply compatible with my slimline computer and take it to my local computer store for assembly. I was told by one of the employees there that my slimline Dell would require a special compatible power supply which would fit in etc. which I would need to purchase on the net.
Sorry, I thought you were referring to a notebook PC. In this case you may have to get one from Dell. They will know what yu need. If I'm not mistaken, their PSU's are made a little different from the rest.
Abz,
the biggest psu for the Dell Dimension C521 slimline is 300w, i think you may have to tranfser your insides to a bigger case that you can put a standard atx psu in.