@danmb 

315W unit from Optiplex XE2 works afaikt YMMV.

D315ES-00 Power Supply  4FCWX / VX372 315W 

Optiplex XE2

DELL 4FCWX / VX372 315W Power Supply

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Hi,

I should have mentioned that this isn't an upgrade, it's strictly a replacement for a bad power supply. And I'd prefer a power supply that's specifically for the 7040 - i.e. it lists the 7040 as a compatible system in the description.

Thanks

Dell Optiplex 3040 5040 7040 MT Inspiron Vostr 3650 3653 240W Power Supply DHJVN THRJK
New on eBay https://www.ebay.com/itm/202252210939

https://www.ebay.com/itm/202395728357

Compatible Part Number: THRJK 4GTN5 4R1KT D7GX8 HGRMH 2P1RD H62JR 3RK5T 6WX7D 0M1C3 J1J77 RKTF0 20WFG 0THRJK 04GTN5 RWMNYu

Note the psu is TFX form factor for 7040 MT.  some vendor lists the slim 240w psu for 7040 SFF by mistake. In Dell original stock configuration 240w is strictly for MT and 180w for SFF.  
https://clascsg.uconn.edu/download/specs/O7040.pdf

@danmb 

The upgrade I mentioned works in MT or DT models and is from Dell and you can see in the video it works fine.  Given the age of the unit Ebay and Amazon etc are the only choices for power supply since Dell doesnt make them anymore.