I am looking for a cable standard to control and power a device from its controller.
I need to send 5V/10A but also control (not sure yet what protocol it could be but I don't need a high speed, 9600b serial could be enough) over short distance (about 2m.) I looked up PoE but it's really not enough in terms of power. Ideally I don't want something too exotic and hard to find.
USB Type C, properly configured, can provide up to 100W and also a means to connect a serial device using the basic DP/DM pair.
More here: How does a USB C port provide the power to charge laptops?
The reason PoE limits the power has to do with the magnetics: the core wires are quite small, smaller than then 24AWG that Cat5 uses, which can carry up to 2A or so per wire.
As it so happens, PoE has seen some upgrades and can now support up to 90W. More here: https://www.versatek.com/what-is-power-over-ethernet/
From your comments on answers, you describe yourself as "new to electronics" and you are unaware even of the ability of different wire gauges to carry current safely.
This is a significant amount of power, with significant risks of things overheating. To make matters worse, you're talking about starting with mains voltages as well, which means you're building yourself an entire mains power supply, and that really isn't a place for novices.
The worst case scenario here is that you burn down your house, and you and your family die in the flames. The next worst case scenario is that you catch a mains shock and kill yourself. The next worst case scenario from that is that you and your family get out but your house burns down, and the insurance company won't pay out for you doing something so blatantly dangerous. All these are not infrequent scenarios when it comes to DIY mains wiring, and that's essentially what you're playing with here.
There isn't a magic secret to working with high-power devices and mains power, the same as driving a car, flying a plane, or any other activity with risks attached. It just needs you to know what you're doing, to know what the risks/issues are, and to take appropriate steps to deal with those risks/issues. At the moment you simply don't know where the bear traps are, and your steps may put your foot in one.
Please don't take this as a reflection on you as a person - it's just that you haven't learnt how to do it yet. With a bit more experience you'll be fine working up to something like this. Right now, I suggest this isn't a good idea.
(Edit to add: I've been working on lower-voltage electronics for about 30 years now, and I've done odd bits of low-key domestic rewiring. I generally know where not to stick my fingers! But if it comes to high-power stuff, or if I need serious domestic wiring done, my first port of call is still getting someone else to do it who's got better skills than me.)
I am taking a SWAG as there is not enough information to completely answer the question. Knowing the loads would help along with a rough schematic. Have you considered the size of the wire you will need. #16 AWG wire at 2 meters will drop about 0.5V, leaving you 4.5V at the end of the cable with a 10 Amp load. This is about the minimum voltage for many 5V devices Try this calculator, it will help you determine wire size as you do not give enough information to do it accurately. I know this is not what you want to do but consider using a 12V or 24V supply with a buck converter at the end of the 2 meter cable, your voltage will be much more stable especially if it is not a constant load, which you did not mention. You can also use a second buck converter at the controler end, that leaves you with one power supply. Considering you were thinking of PoE by using buck converters you can up the voltage, and reduce wire size even more. OOPS the calculator link did not stick here it is: https://grealpha.com/resources/dc-load-wiring-calculator/calc/voltage-drop/
Here's an idea to keep things simple and save some money: put the power supply in the device, and power the controller from the device. Doing anything else is likely to require two high power conversion stages instead of one.
I'm assuming you're powering everything from the mains, the device needs 10A at 5V, and the controller needs 5V and minimal current. Now ideally the device would be what plugs into the mains, but if you want the controller to be what plugs into the mains, then there's no reason the mains power can't just pass through the controller and then down the cable to the device. An ordinary mains flex will answer the purpose, but consider that you'll need an earth if the device is not double insulated. Then you need to send 5V back to the controller, and establish a serial link. An inexpensive CAT5 cable could answer both purposes. Use one twisted pair to send 5V power back from the device to the controller. Use another twisted pair for the serial link, or two pairs if you need bidirectional communication.
Now you have two cables, when I'm sure you wanted an elegant solution with just one. You could wrap the two cables together with a braided sleeve. This isn't ideal to send power and data together because of the potential for interference, but you only need a low data rate anyway. For better noise immunity you might use differential signalling for the serial data and maybe put low pass filters on 5V power with enough capacitance at the controller end to ensure stable voltage. If you have a 3D printer you could make a connector housing that combined an IEC connector for the mains power with your choice of low voltage connector into an elegant single unit.
There are a few companies that make rather expensive "hybrid cable" that has either 2 or 4 100-ohm twisted pairs for ethernet and 4x 16AWG wires for power. Harting and Lapp come to mind.
I looked up PoE but it's really not enough in terms of power.
IEEE 802.3bt-2018 aka 4PPoE provides up to 71 W (on 100m cabling).
The truth is that there is no commonly available cable for this.
An easy and reasonable solution is to use a connector that can handle 10A per pin, and get one with enough pins for the power and data, even though the data doesn't need large pins.
If you make your own cable using these connectors, you can make the conductors for the data appropriately sized.
Edit: You should also explain why you can't just use 2 cables bundled together.
