The problem it's a device I am modifying, so I am not really free to just alter it's voltage like that.
You could be modifying - the device has a 5v requirement , you can easily add a small pcb with a dc-dc converter that takes in a wider range and outputs 5v for the device.
Could be as easy as cutting the traces under the barrel jack connector of the device, soldering your wires going to your dc-dc converter then soldering the two wires from your dc-dc converter's output (5v) to the traces originally going to the barrel jack.
OR, if possible, you can remove the barrel jack from the original pcb, and solder wires where the barrel jack was, and then use a different barrel jack (maybe one that can be screwed to the case)
You can buy separately cable with usb type a on one end and loose wires at the other, so you could quickly crimp a barrel jack connector to the other end to make your custom cable.
Don't those cables max out at 2A though? I wanted to at least get a 3A power supply.
They're rated for maximum 2A because of the wire gauge and because of the voltage drop across the length. Most such cables use AWG24 or thinner wires, so the longer the cable length the higher the resistance, which means more voltage drop at higher currents.
For example let's say you use one of the cheaper 1m cable with AWG24 wires for the power ... that means you have 2 meters of cable between psu and device in total, and the awg24 wire has a resistance of 84 mOhm per meter.
So at 2A of current, you have 2A x 2m x 0.084 = 0.336v drop on the cable ... your 5v is no longer 5v, it's 4.664v at 2A - For USB the requirement is minimum 4.75v so such cable would only be good for 1A of current.
There's cables that use AWG22 or even AWG20 and even AWG18 for power, but those are more expensive.
For example charge only (so only power wires) usb type-a to type c for 2.5$ using AWG22 wires :
https://www.digikey.com/en/products/detail/globtek-inc/USBA2C1MOUSBC-R/12546298Or this extension is 1.83 meters (6.00') and claims to use AWG 20 for the power wires :
https://www.digikey.com/en/products/detail/coolgear/USBG-AA6CC/136845393A at 1.83 meters on AWG20 wires that have 33.3 mOhm per meter = 3A x 2 x 1.83 x 0.0333 = 0.365634 v drop across the cable at 3A - at 2A it's only 0.243v
With higher voltage like 12v, you have much lower current on the cable, so much less voltage drop ... a 12v 1A adapter gives 12 watts, even with poor 90% conversion efficiency, you still end up with 5v @ 2A = 10w available to a device.
Yeah, I tried going through that list. Thing is those started out at 1A. when I sort by 3A and larger in stock, there is one $10 one and the rest start at $13-15
The problem is the voltage drop on the cable at such high current. They'd either have to use thick wires (AWG18 for example) OR they would have to add a third sense wire to measure the voltage at the plug and adjust output voltage to keep output at plug at 5v - that adds complexity.
Yeah, a lot of these seem to be designed for a UK market. Which doesn't really help me much since I am in the US and even with the plug issue taken care of sometimes shipping alone can cost a fortune.
As I showed you, you can buy those adapters with removable AC cable, and then you can use your own AC cable with US plug.