basc psu calculator shows one does not really need the 1350w psu for i9-13900KF, 32GB DDR5, RTX 4090, NVMe SSD

Lod Wattage:769 W
Recommended PSU Wattage:819 W

nor does R13 need 1350w psu to run i9-12900k and RTX 4090, which suggests R13 user can run the 4090 using the 1000w psu.

Load Wattage:758 W
Recommended PSU Wattage:808 W

This is also corroborated by techpowerup spec on Dell oem RTX4090: suggested psu 850W

In case someone wonders, the R15 proprietary 12 pin motherboard socket is built on the R13/14 10 pin socket. The extra 2 pin likely provide more 12V power, and pinout are likely +12V and Gnd.  The 10 pin 750/1000w psu of R13 are compatible w R15 motherboard which was mentioned in spec.  You can plug the 10 pin connector of 750/1000w into the R15 motherboard 12 pin socket as illustrated in R15 service manual.

The 10-pin connector belongs to older R13 while 12-pin connector belongs to newer R15. The 12-pin connector is just the 10-pin cable with 2 extra wires to provide extra current. As long as your power supply can provide sufficient power to the motherboard, you can still use 10-pin power supply. 

thank you for this!  Does this indicate that this psu will not work in an R13 (as its 10+4+4)?  Maybe there is a 12 to 10 adapter?  Also, in the picture I do not see the 12VHPWR gpu power cable?

good question.  I think you may be able to physically plug a 12 pin connector in 10 pin socket of R13.  The extra 2 pin would be unused hanging in air.  This is like plugging an 8 pin eps connector in a 4 pin cpu socket of some motherboard.

I think one way to try to answer this question is to go back to 24 pin ATX.  Some older ATX power motherboard use 20 pin socket. For that reason some psu makers design their 24 pin connector to be splittable 20+4.  Based on that reasoning I think there is a good chance the 1350w psu 12 pin connector would electrically work with R13 motherboard 10 pin socket too.  Ultimately it would be nice if Dell engineer or some one can validate this before user purchase the 1350w upgrade.

I do not know why Dell designed an extra ostensibly unneeded 4 pin cpu connector for the 1350w psu.  Can this be a backup 4 pin connector if one of the first two do not work. strange.

Will be interesting to see the 120 VAC requirements for a 2,200 Watt PSU.

For those interested checkout the certification result of 1000w vs 1350w oem psu by Delta

https://www.clearesult.com/80plus/sites/80plus/files/manufacturer-certificate/dell-d1350epf00-11572.pdf

https://www.clearesult.com/80plus/sites/80plus/files/manufacturer-certificate/dell-d1000eps00-11573.pdf

No ATX 3.0??

BWAHAHAHAHAHAHAHA!

It uses psu extension cables to meet ATX3.0 standard: 12VHPWR+ 2 sense pins. The psu itself still uses two GFX cables each having one 8 pin and one 6+2 pin piggyback connector.  The numbering goes GFX1-4.  The extension cable for 4090 12VHPWR is GFX5.

hmm, so with only 2 physical power feeder cables, this means the psu cables are spec'd to handle the potential 300 watts each for an overclocked 4090, as the 12vhpwr adapter cable internally just connects all positive and negative leads together.  I also read that one can lower the power draw of the 4090 by 80% and still get like 99% of gaming performance out of it, even 75% reduction yields like 97% and doesn't make a dent.  Given this, by using a 6 to 8 pin adapter, I can easily run a 4090 off my day-one R13's measly 750 watt power supply.  Go with a 4090 FE, as one fan grabs air from the top, remove the psu shroud for the other fan, should be good to go, just need the 20% sale and I am in!