Looking for Optiplex Power Supplies

That is really what I don't want to do. Run around and try and find a used one somewhere. I think all of them (HP, Acer, Dell, etc.) are somewhat proprietary but you can't really tell. There is SFX, TFX, Slimline, ATX. The list goes on and on. I am looking at a Optiplex 3040. it has 1 - 2x2 for the CPU and 1-2x4 for the motherboard. Even looking on Amazon you don't see anything over 240W.   

You can get high power systems in the Alienware line that Dell also owns.  Not cheap.

Not really what I am looking to do. Want to upgrade the power supplies (wattage) in their Optiplex line.

With the major OEM's you get what you ordered and that's pretty much it. The cases, motherboards, power supplies are all proprietary. What they offer is good enough for about 70-80% of the computer users. The power supply is just fine for the hardware installed. The other 20-30% of the users use off the shelf components that follow industry standards. A power supply is one physical size and has the industry standard connectors same with motherboards.

This standardization with every item minimized is how the major OEM's keep their prices down.
Dell has multiple product lines. Optiplex and Precision are for business customers while XP and Inspiror are for home consumers.

If you had a dell precision that is meant for CAD you would probably have been offered a more wattage power supply.

   That is a true statement. I have been saying that for the last 30-years. Get what you want up front because you probably won't be able to add anything after-the-fact. Usually you can find someone who will manufacturer specialty after-market products but only if they can make a buck. This looks like one of those time where they can't make a buck.

Side note:  The cooling control on recent Dell power supplies is, I/M/O, not well designed.

I upgraded an Optiplex 980 with a Radeon video card and while it was only a 50 watt card, the heat generated was significant.  This would have been fine if the fan was running steadily   But to reduce noise there's a heat sensor in the power supply and the fan didn't accelerate until the temperature in the case got well over 100 degrees.  Meanwhile there was uncomfortably hot air lazily drifting out the back.

Eventually I had to open the supply, disconnect the fan control completely, and stick in a manual fan speed control with a control knob.

In some other Optiplex the heat sensor is down at the bottom of the case.

If the PS connector on the motherboard matches a standard PS connector both in physical size as well as wiring colors (VERY important to check the latter), my experience has been that a standard PS will work.  It won't fit the case, but it will power the system.  I've done that a number of times when the PS has failed and I needed to get it running right away.  It's not very elegant, but it can work!

Thanks Gents