This system does not need a 750W PSU, and even if it did, I wouldn't suggest the corsair CS750M.
How big of a graphics card are you planning? A GTX 980? MSI suggests 500W for their Kick-A High end graphics card that probably won't even fit in the case.
Research this more. Speedstep has a bunch of out-dated, copy past text that doesn't apply to haswell motherboards.
I run Seasonic X-650s in two XPS 8700s, with high power draw graphics cards. Overclocked GTX 770 and an overclocked GTX 760. If seasonic had a high quality 550W I would have bought it.
Also, that Corsair is just an average PSU. There are better units for the same money or equal units for less.
Here is one that is (in my opinion) better and less money.
the physical dimensions of the case would be the limiting factor, but i intend to at very least have a video card with at least 2GB GDDR5, preferably 4GB GDDR5, with a core clock at least 1000Mhz, preferably beyond that, i also intend to insert the most powerful CPU i can fit in there, which looks to be the Intel Core i7 4790k, double the ram to the max, and be able to sit back and play Elite Dangerous, and games of that magnitude. (i have a fair number of games on Steam), i also intend to render CGI animations via Blender and the like, so the more umph, the better. i have found cards such as http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=9088213&CatId=7387 .
Why not buy or build a new machine? By the time you add upgrades in the $600 to $900 range, spend another $150 and build a complete system.
You mentioned a 4790K and a video card that will run A-list games. I think a GTX 960 is the low end of this and a GTX 970 is the sweet spot. You mention CGI rendering. These applications are memory hungry and 32GB will help this out along with large, very fast drives, and maybe multiple SSDs (an SSD scratch disk)
But first lets look at how far you can push the 3847.
The hard disk mounting location will interfere with a full size graphics card. It looks like this could be worked around by moving one HDD to the second 5 1/4 inch bay and mounting an SSD underneath it. SSDs are easy to mount in lots of places.
The other option is a short form factor graphics card. Here is an example:
But the fullsize cards are quieter, run faster and overclock better, but even moving the HDDs it might be a challenge to get a full size graphics card in the inspiron case.
Cooling is an issue. Read the XPS 8700 / GTX upgrade thread that has been going on for almost a year. Many of us have GTX 970s or GTX 770s and a few GTX 980s but when pushed hard the cases are getting warm to hot. I think the XPS 8700 case is setup to breathe better than the inspiron case but maybe an extra intake fan can solve this. There is one who added fans to the 8700 and the temps got worse so YMMV.
CPU: I've yet to see a 4790K installed in a 3847, but it might work. There is a recent post in this forum where a 4790K was successfully installed into a XPS 8700 with a water cooler so it looks like anything might be possible. The downside I can see is the 3847 motherboard is not built to supply the power that the 4790K needs.
The 3847 motherboard tops out at 16GB RAM with only two DIMM slots. Plenty for games but may limit the CGI rendering. Also I think the 3847 has only two SATA III connectors and the rest are SATA II so if you plan more than two SSDs you should factor that in. Most HDDs don't push the limit of SATA II.
So back to the power supply: I suggest you do get a 650w or 750W, 80plus Gold fully modular power supply because I think once you start upgrading this computer you'll out grow it and then you'll have a great PSU to put into your next build.
Or skip the upgrade and start saving for the next build and buy the parts that match the needs of the system.
Once you upgrade PSU, RAM, CPU, Graphics card, add SSDs all that remains from the original system is the case the motherboard and maybe the wifi/bluetooth. A decent case can be found on sale in the $50 range, and a really good case can be found on sale for around $100. Solid Z97 motherboards built for overclocking are in the $100 range.
Just a thought.
The corsair supplies are not misleading. People are misleading themselves by thinking of a power supply as linear and a single 12v rail with single specification of Watts. Saying you can use a 500W for a 970 or 980 is disingenious at best. Even Dell 305W units have specific loading balance not just 305W on 12v and throw the baby out with the bath water.
Dell doesn't overstate what their power supply can do. Smaller NON EPS12v power supplies do not provide 170W on the 3.3v and 5v rails and 20 to 25W on the 5vSB rail. Getting smaller means the supply might not work at all or will blink Amber within 30 seconds of turning on.
5.0V @ 16 A = 80W
3.3V @ 8A = 26.4W
12V @ 25.0A = 300 W
5VSB @ 4A = 20 W
Dell Rates as a 305W power supply.
This also assumes 80% or better efficiency. Aka 100W = 80W at 80% efficiency.
Many of the Cheap NON EPS ATX power supplies that people choose based on PRICE only provide 15W on 5VSB and 120W on the 3.3/5 rail which means in some cases it won't even turn on or if it does it goes to flashing amber within 20 seconds.
The 550M may be too small if you use a Pentium D 960 because the 5VSB is 15W not 20W. S3 standby may need as much as 30W for some processor/motherboard configurations. If you add up the max power ratings at the bottom you get a much larger number. You ignore ratings other than the 12v rail at your own risk.
I installed a 4790K in my 3847 and a Geforce 570TI SHORT card and a Corsair CS750M and it works fine. Max ram is 16 gigs as there are only 2 slots.
@Speedstep, I am not saying Corsair's PSU stickers are misleading. Corsair would be crucified by the aftermarket reviews if their power supplies don't measure up to what is on the sticker.
I am saying your comments to forum members that EPS 12V spec PSUs are required is misleading and inaccurate.
EPS12V is a server specification and while an EPS12V rated PSU might work in a desktop the specification is not required.
The correct desktop power supply specification is ATX12V version 2.x where preferably version 2.31 or higher. Intel folded all of the various sizes into a single document and then very clearly states these are guidelines not a hard requirement.
so here are the specs.
-- The EPS 12V specification is very clear as well as the intro:
Power Supply Design Guide
A Server System Infrastructure (SSI) Specification For Entry Chassis Power Supplies
1 2 Purpose
This specification defines a non-redundant power supply that supports entry server computer systems.
- - -
In contrast the power supply design guide from Intel, which references the desktop specs including ATX 12V 2.X, allong with SFX and other form factors for desktops.
- - -
Power Supply Design Guide for Desktop Platform Form Factors
This document provides design suggestions for various power supply form factors. The power supplies are primarily intended for use with desktop system designs.
I disagree and will continue to disagree with you when you state as fact that Power supplies must be EPS12V because this is inaccurate and misleading.
Some power supplies meet both specs however there are many that are good that do not certify EPS12V and this does not rule them out as a viable PSU.
I didn't try to use the plastic fitting Press on intel retail cooler. I replaced the thermal compound with arctic silver and put the stock cooler back on. It works fine. I chose the video card based on physical fit. Its an EVGA GeForce GTX 570 HD 1280 MB GDDR5
012-P3-1571-KR The card is 8.7 inches long and barely fits in but it does fit without modding the case and drive bays.
thanks for the info on the CPU, i did also find a couple of powerful GTX 900-series models that would fit in the space
$300 for the 970 is more than I am willing to spend. The GTX570 was $100.
For what I need its good enough. Both those cards seem to be the short variety so if they are less than 9 inches long and the power connector goes in via the top then you are good to go.