Dell Optiplex 990 Sff Power Supply Upgrade

How to install change replace upgrade power supply in a dell optiplex 390 790 3010 7010 9010 sff.
Dell optiplex 990 sff power supply upgrade. I do not work for dell. 1 power supply for dell optiplex sff 3010 7010 9010. Gotta get crafty but no big deal. Thx for helping me.
Here is the list part upgrade power s. Looking for a power supply upgrade for my optiplex 990 sff so i can install a decent graphics card. 4 gb 2x2 gb ddr3 1333 mhz graphics. This item 400w power supply upgrade for dell slimline optiplex 390 790 990 7gc81 6mvjh thermaltake smart 500w 80 white certified psu continuous power with 120mm ultra quiet cooling fan atx 12v v2 3 eps 12v active pfc power supply ps spd 0500npcwus w.
I am also a user. The power supply has to be equal or smaller than 9 5 by 2 8 by 2 4 inch and produce more than 400w thanks in advance. Intel core i5 2400 3 10ghz 6mb memory. The original plan is was to transplant the system into a bigger case.
But its some funky size mobo. Just wondering if i can upgrade my dell optiplex 990 cpu from a i5 2400 to a i7 2600k. Will any atx power supply fit in the 990 minitower. On newegg the sizes of the various power supplies seem to be slightly different dimensions than the dell optiplex 990 supply.
I have a dell optiplex 990 sff small form factor processor. So its not that cut and dry. I was wondering which power supply fits the sff and is 300w or 400w. Only mini tower dell s can use atx power supply upgraded elpro999.
What im wondering is will this computer accept a larger power supply. Optiplex 990 sff psu upgrade. Hi i just got a new graphics card for my optiplex 790 sff and it requires 300w power supply. The system comes with 265 watts but i d like to install a more powerful supply so i can upgrade the video card to whatever i want.
I picked up a super cheap optiplex 990 sff with an i7 2600. I saw many people saying that the i7 2600 is compatible but i want to know if the i7 2600k is compatible due to me wanting to possibly overclock in the future once i upgrade.