"I have pots to adjust the voltages += 10% because the hardware it's for is supposedly very finnicky with voltages." If your load is that fussy about the exact output voltages that you need to have adjustment pots then the circuit you are intending to use as a power supply is going to be pretty rubbish. "First off, I'd just like to ask if the circuit makes sense? is there anything obvious I'm missing here?" Well, you asked. The reason your circuit is pretty rubbish is because although the LM317 output voltages are closely regulated, the output voltages from the emitters of the 2N3055 transistors are not. The output voltages from the emitters of the 2N3055 transistors are not regulated because there is no negative feedback loop controlling the output voltage. Although the output voltages of the LM317s are regulated, they are passed through the series diodes and the base emitter drops of the 2N3055 transistors and these voltage drops will increase with load current and will changes by about 2mV/degC for each device. Everything about this "PSU" circuit is just badly designed. The series diode allows the transisotr base current to increase rapidly if required but may stop it reduing quickly when the load current drops suddenly. There are no decoupling capacitors anywhere in the circuit. There is no short circuit protection for the outputs. The 3.3V output is passing 12A. So your 3.3V load is dissipating 39.6W. Neglecting the power dissipation in the LM317 which is probably supplying about 1A base current to the transistor, the transistor is dissipating (12V-3.3V)*12A = 104.4W. The LM317 will have to be set to output about 1.4V higher than 3.3V to allow for the diode and transistor Vbe drops which will be around 0.7V each so it will be dissipating  (12V-3.3V-1.4V)*1A = 7.3W. The diode and the base emitter junction of the transistor will dissipate another 1.4V*1A  = 1.4W So for a roughly 40W load you are burning over 110W as waste heat! You can do the same sums for the 5V output which is not quite so bad but for a 60W load it is still wasting about 90W. That is hopelessly inefficient and will need massive heatsinking, probably with forced air cooling. You would be well advised to read the LM317 datasheet and study the example circuits in it, which include some designs that could be adapted to and would far better suit your requirements: [http://www.ti.com/lit/ds/slvs044y/slvs044y.pdf?ts=1588798780682](http://www.ti.com/lit/ds/slvs044y/slvs044y.pdf?ts=1588798780682) Having said that, at the powers you are dealing with, unless you have a _very_ good reason for needing the low noise you can get easily from an analogue regulated power supply, you should be looking at a switch mode PSU design. In fact you could probably buy an off the shelf PC supply that will already give you these outputs well enough regulated for your needs. And it will come with a universal mains input. For example: [https://www.ebuyer.com/951101-corsair-cv-series-cv450-450-watt-power-supply-cp-9020209-uk](https://www.ebuyer.com/951101-corsair-cv-series-cv450-450-watt-power-supply-cp-9020209-uk) About the only thing you need to watch is that you always draw the minimum load from each rail to stop it drifting up too far. If necessary that can be done just by adding extra load resistors on each output. If you are prepared to consider wasting 200W with your current circuit then a few tens of watts for the minimum load resistors can be considered as hand warmers. You should also note that the 6A4 diode is not recommended for new designs: [https://www\.diodes\.com/assets/Datasheets/products\_inactive\_data/ds28009\.pdf](https://www.diodes.com/assets/Datasheets/products_inactive_data/ds28009.pdf)

@andyfierman Thank you for the honesty, I appreciate it. It seems I'm coming at the problem in a completely wrong direction. All I want really is a way to fine tune 5v and 3.3v, the arcade board I'm trying to power supposedly blows up above 5.15 or below 4.8. which is better than ATX spec. 3.3v should be about as exact as I can manage. I'm going to try again, and have a good look into everything you've said. Would you recommend I look at emulating example circuit 9.3.12 for my needs in the datasheet you linked? Or would there be another way to achieve what I'm trying to do? Thank you for the advice and help so far.

With any linear regulator design supplied from your 12V PSU, you will still have those huge power dissipations. A better solution would be to design a 12V to 5V 12A and a 12V to 3.3V 12A step down switch mode supply. More or less once you have one designed the other is not going to be too far different. Or just buy them off the shelf. If the design of a couple of 12V to 5V 12Aand 12V to 3.3V 12A step down switch mode supplies seem daunting, you still could consider using a PC PSU but something with a 3.3V output at around 30A from which you draw the 12A at 3.3V and from which use a 3.3V to 5V step up switch mode supply using a 1% reference and 1% resistors (1% or better) to get to a (5.18V-4.8V)/2 =4.99V nominal. But that's nearly as much work as designing the two step down supplies anyway... A switch mode supply is however a harder thing to design and layout. If you choose a suitable converter with a good datasheet and apps notes you can get there reasonably easily. Choose the right type of device and it can be simulated to give you much greater confidence in your design. With a good design you need not be but if you are worried about the ripple from a switcher, one option is to design for a slightly higher output voltage and then use a low drop out linear regulator to regulate down to the 4.99V with a tolerable power dissipation in the linear regulator. In practice you should not need to do that as there are better ways to keep the switcher ripple within reasonable limits.

A bit tricky to assemble onto a PCB but something like this is an extremely cost effective solution: [https://www.analog.com/en/products/ltm4626.html#product-overview](https://www.analog.com/en/products/ltm4626.html#product-overview) Or, easier to assemble onto a board: [http://www.ti.com/product/PTH12010W](http://www.ti.com/product/PTH12010W) JLCPCB don't seem to stock it but it might be worth asking their support. [https://jlcpcb.com/parts](https://jlcpcb.com/parts) There are many other places that do things like this but beware buying unbranded stuff from non-specialist electronics suppliers which does not have a datasheet up to the same sort of standards as Analog and TI. They may be a lot cheaper but sadly are often junk. Buy from places like LCSC, Farnell, Elelment14 and RS (not Radio Shack!) if you can.