Depending on what pre-built OEM computer you have, there can be a few potential issues.
Often, if the pre-built is using standardized measurements such as a normal ATX size case, as one example, it should be possible to install another PSU without encountering a lot of problems, if any.
Other times, some pre-built manufacturers use uncommen shapes and sizes for the connectors, and sometimes uncommon sizes of their cases, in which case it is difficult to make a direct upgrade of the PSU with off-the-shelf components.
I'll try and look-up a Dell 580, I'm not familiar with this particular model, so I can't say what is possible in your situation
EDIT : According to
this question on the Dell official site, it should be straight forward to upgrade the PSU to something different
Only thing I notice is, that it is aparrently a small case, so a fully modular PSU would be recommended, to avoid cable clutter which could reduce airflow and decrease cooling performance as a result of that