@geoffbates wrote:How can I tell what will fit?
Should be standard ATX. 5.9"(W) x 3.4"(H) x 6.3"(L) or smaller and you will be fine.
Modular recommended, tight fit between the PSU and the optical drive bays.
R Series Radeon or RTX NVIDIA cards are not working in an XPS 8300 EVER.
ATX is not correct. EPS 12v with 150W combined 25A on 3.3v 5v rails is required.
Nvidia up to and including 1080TI work but require larger power supply.
GT 1030 up to GTX 1050TI work fine with stock power supply.
EVGA 700B1 works B2 BQ N1 W1 etc from same vendor DOES NOT WORK due to insufficient power on 3.3v and 5v rails. Modern PFC power supplies are 80 percent efficient and EPS 12v Spec.
CX750M also works.