Powersupply Does Not Fit In Case

Yes, return it and purchase one made for your case.

You can also find them  online but be carefull. I purchased one online from a company in Tx a few months ago. It was made for my dell, but would not work. I found a used one and it worked perfectly.

Hense short of returning it.

nada

Just cover the open space with something,

As long as all the screw holes line up allowing the PSU to be properly secured (flush against the bottom of the case) and none of the fans are blocked I don't see any issues keeping it.  You may want to plug the whole that is left if it disrupts your airflow within the case.

If the PSU is not flush against the bottom or screw holes don't line up there is always the option of drilling new holes to make it fit or returning the unit for another that will fit properly.

It could depend on how much cheaper the Coolermaster PSU is compared to the Dell one. If the price difference is noticeable and the back of the computer isn't normally visible, I'd just cover the gap with some gaffer tape and carry on. If it is visble, I might make a bit of an effort to make covering the gap more aesthetically pleasing, but then again I might not...

That's the bad thing about Dells, they're not made to be able to easily swap out parts, unless they're OEM.  I'd stick with the Coolermaster, just find something to cover the gap.

did you use it already -and it works?  some have other connections; so be sure to verify that first

Has this issue been resolved?

No, Is there a 3rd party panel that will cover the hole? Where can I get an official Dell one?

You can go to ebay, enter the PS model and find rebuilt units. I've done that before and they always worked well for me.

The PS model is on a sticker on the PS.

>>  Is there a 3rd party panel that will cover the hole? Where can I get an official Dell one?   <<  if the ps not Dell  -then Dell does not provide a panel for other PS'es
i doubt you'll find a panel  - but why should it be covered up?  surely it does not harm ?

Why can't you create something yourself to cover the space? It should be easy enough to do...

Glad I could help