The following should help.

https://www.dell.com/community/XPS-Desktops/XPS-8900-PSU-upgrade/td-p/7287823

https://www.dell.com/community/Desktops-General-Read-Only/XPS-8900-PSU-Upgrade/td-p/4734759

https://www.dell.com/community/Desktops-General-Read-Only/XPS-8700-Graphics-Card-Upgrade-and-PSU-upgrade/td-p/5075588

JOcean,

Thanks, yes I stumbled on those in my searches. Someone else where mentioned something about needing an adapter (I think 24pin to 8 pin) to accommodate the connection to the motherboard in the Dell? Is that accurate? Aside from that would it just be a plug and play swap using an aftermarket PSU to replace the factory Dell one, or will there be issues? I have seen elsewhere something about connecting to the Dell power button being an issue. Not sure on the specifics of that.

The 8900 series does not need a 24 to 8 pin adapter.  It may need a 15 pin to 6 pin sata power cable if you have an optical drive that is the smaller size.  24 to 8 pin or 24 to 6 pin is for other models like optiplex or inspiron.

https://www.amazon.com/CRJ-15-Pin-Slimline-Sleeved-Adapter/dp/B07FK5G2TF/

Only specific 89XX or Aurora or Inspiron models need the 6 pin laptop style power cable.  The 8920 or 8930 for example.

The 600BR is not sufficient due to only 130W on the 3.3v/5v rails.  EVGA 700BR is fine 600BR is not.  The Stock Dell 460W has 142W on this rail set.  Other Dells need 150W combined on this rail set which is why the 700BR or 700B1 from evga is recommended minimum.  G2 B2 BQ N1 W1 versions from the SAME VENDOR do not work for that reason.  Power supplies are not single rail with single spec of watts.

https://www.bestbuy.com/site/evga-700w-atx12v-eps12v-80-plus-bronze-power-supply-dc-dc-technology-black/6346160.p?skuId=6346160

That is also why its $20 or so more expensive.

Thank you! 

Turns out I have a corsair Tx750 80+ PSU from a build I did prior to getting the 8900. Would that work (saving me the $80 purchase of the one above)?

I have a Dell XPS 8900. I am interested in upgrading the GPU to a Nvidia 2080 Super however the card requires a 650 watt PSU. I am interested in anyone who has upgraded the PSU on their Dell XPS 8900. What did you manage to fit inside the case? Please let me know. 

Thanks

EVGA 700BR fits and works.

TX750 should work if it has 24 Amps on 3.3v and 150W combined on 3.3v/5v rails and its not too long.  Its a very tight fit in the case.  The USB ports on the top get in the way if the psu is too long.

https://www.evga.com/products/product.aspx?pn=100-BR-0700-K1

https://www.bestbuy.com/site/evga-700w-atx12v-eps12v-80-plus-bronze-power-supply-dc-dc-technology-black/6346160.p?skuId=6346160

EVGA 750B1 fits and works but its hard to find now??

B2 BQ G2 N1 W1 versions from the same vendor fit but do not provide sufficent power on the 3.3v /5v combined rails.