Is it plausible to upgrade a PC power supply to deliver more current?

tl;dr: I have a small form factor PC, and the biggest power supply it will accept only puts out 500W, while my video card needs 600W.

I thought to myself: What if I upgraded the transformer and uprated the filter capacitors? Could I get more out of the supply? Or would it become an endless series of upgrading each component to a higher rated value?
 
I've done quite a few custom cheapo PC's, custom cheapo as in soldering iron and rivet gun.

IME trying to upgrade the stock PSU is likely the worst way to go. If the PSU is proprietary in that size and shape are nonstandard, remove internal metal pieces by drilling out rivets and drilling holes until a standard PSU fits. If the PSU is proprietary in that connectors are not standard, try to find an adapter, or see if you can find the pinout and solder your own adapter. I've gone so far as to use 2 PSU's, using the proprietary PSU to power the MB and adding a standard PSU for the GPU; you just wire the sense wires (green on ATX) together. Note that this only works if the proprietary PSU is using momentary on switch logic.
 
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No you cannot modify an existing supply. Anyone making a product in the quantities of any PC power supply has optimized it as far as they can.

To change the design to more power would require a new transformer, then most likely larger driver transistors and filter capacitors. Most likely the rectifiers could take the increased current. But I would expect a bit more heatsink. Now the supply would most likely require 20% more volume, thus a larger case.

Now where you would even get a larger switching power supply transformer in quantities of one is probably an insurmountable problem.
 
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before 2003, i have been working on AT and ATX psu. i have converted an AT into an ATX, one easy mod for any ATX psu is using bigger mains filter caps, i have used 1500ufd/250vdc filter caps....then using more robust secondary rectifiers...how do we know it worked? take any psu that made the pc go into BSOD, modify it and then try again, if the BSOD did not occur, then you know the mod worked, sometimes an ATX psu did not go past the bios POST, modding the psu made it load windows....
 
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I assume 600W is the total PSU power suggested by the manufacturer. You can get away with less in most cases, assuming the card's not under full load constantly and the original PSU is decent.

In extremely budget PC builds (like $150-200 builds) cheap, quality PSUs are hard to come by, so people have to be a bit "creative". By creative, I mean they just duct tape 1 shoddy PSU onto the top of the PC case to power the GPU, with the other responsible for the other components.
 
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The quick answer to the original question is NO: the upgrade as described by SoaDMTGuy is not possible. The complete answer is: maybe, if some conditions are meet, and you are prepared to spend more than the price of a new standard power supply. The good news is that maybe you don't need a 600W PSU at all.

I've assembled, repaired and upgraded hundreds of PCs and I've sometimes modified non-standard PSUs, but only on special circumstances. Most SFF Shuttle PS's are well built nice computers, more expensive than regular ones, so I understand why the original poster want to keep it. I assume that it already tried the new graphic card on the available 500W PSU and found instability, because this is the first thing to try on a quality PC. The graphic card manufacturer 600W guideline is a generic recomandation that is mostly there to exclude the fake 500W or 550W no-brand PSUs that are fitted as standard on most low-cost PC cases. They actually are the very old 150-200W PSU design that has been a de facto standard on office/budget PCs since last decade, with a new fancy sticker and a extra graphic card connector tied to the same 12V output of the CPU core and mainboard connectors. If you try to use this kind of fake PSU on a PC with a 85W+ processor paired with any midrange GPU, the system will shut down randomly. Some cheap PSUs of this kind are so bad, that the PWM controller chip goes out of the regulation loop before shutting off the output, and if you look with the digital scope you will see for several milliseconds 4-5V on the 3.3V output and 15/16V on the 12V output. This may cause damage. RAM sticks are usually the first victim, SSD is the next.
The SoaDMTGuy approach will not work because bigger transformers aren't available as spare part (you need to cannibalise a PSU to get it) and will not fit on the PCB ; also the protection circuit must be altered, and this is not a easy task. It is still possible to increase the power output by gutting the original PSU and transfer inside the empty shell an entirely new one. The PCB inside modern PSU with latest semiconductors are smaller than the older ones, so it may be possible to fit a standard a 600W or maybe even a 700W PSU PCB inside the shell of the old custom PSU. Proprietary connectors must be managed with adapters.
 
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I can't visualise a graphic card that needs 600w...!
There are now a few GPUs (such as Nvidia 4090) with peak power draw over 680W, and you need to add to the total the power draw of auxiliary chips too. A good matching PC power supply should be in the 1 Kw range or more, bare minimum is 750W but then power limits must be set on the drivers.
 
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About the only successful mod I've done on stock PS is replacing the fan. And even that is a challenge. They pack those things tight. I had a couple shuttles years ago and the fan on both went out. Just opening them was challenging and after I got them open, found the only way to replace the fan was to add one on the outside silicon glued to the case at the fan vents. The AT supplies have more space and I have managed to open and replace the fans in those. Wish they'd make that easier. Fans fail frequently.
 
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1) No, it's likely not practical, but anything is possible.
2) I'd be shocked if your video card alone requires 600W alone... unless at peak loads. If it does, then you'd need to increase the power beyond 600W (a 20% increase in and of itself) just to have power for the rest of the components in the case.

It sounds like you want straight answers, and you know your gear even if I have doubts.

tl;dr - if you want to use that card with whatever you've got, I'd look to other solutions.