blokewhoknowsnothingabouttech :
From what I've seen on the internet, it is possible to fit an aftermarket PSU. Dunno if you'd need an adapter though. I'm more concerned about front panel connectors, how'd you think that'd work?
Robert,
Due to the age of the motherboard, the key factor is possible differences in the connectors. I had that situation when adding a PERC H310 RAID controller to a Dell Precision T5500 which predated the H310: the HD activity LED lead was four-pin on the H310 but was three pin on the T5500 front panel. There is still no HD activity light on the T5500. By the way, have a look at the PERC H310 as it may work in the 390 and that would increase the disk subsystem from 3GB/s to 6GB/s. On the T5500, the Samsung 840 Passmark disk score changed from
1940 to
2694 without any other change.
The other concern would be the USB ports. Have a look at the connectors on the 390 and see if it possible to download from the manufacturer's site, the detailed parts list for the proposed case. However, if you have the PCIe slot open, consider adding a PCIe USB 3.0 card and that will provide USB 3 and 2 to the front panel and have a couple of each on the rear panel.
It might also be possible to salvage some of the front panel parts from the 390 for transfer.
Is the change of case to be able to use larger GPU's?
Cheers,
BambiBoom