Unless you are prepared to build some industrial strength equipment of your own design and then move everyone in the neighborhood away while you experiment with this, I fear you are taking your life in your hands.
Normal pressure cookers add a maximum 15 PSI to achieve a water boiling point of 121 C or 250 F. Autoclaves, used for surgical sterilization, go to 30 PSI. You are talking about going more than twice that.
There is no reason, based on the science of Maillard reaction, to believe that it would not occur at a high enough temperature. The presence of excess water would normally inhibit the process because of temperature reduction, but your "super duper pressure cooker" would keep the temperature at a high enough level to allow the chemical breakdown to occur. You might, in fact, discover that it occurs a bit earlier, as water tends to facilitate many reactions. Caramel making comes to mind as an indicator of what might be achieved, as sugar syrup (OK, most of the water is gone, but in principal) browns when you get in the above 330F-165C degree range.
As to crisping based on quick pressure reduction (perhaps when your device explodes?) That seems less likely as most crisping comes at the loss of water, and you are, in effect, keeping water in contact with your food both in liquid and superheated steam form. It would, most likely, be similar to a braised food surface, than a fried one.
Interesting thought. Please don't try this.
Pressure cookers and pressure canners are the same thing; with the canners being larger, and often having a pressure dial. Both can reach the same pressures and therefore temperatures if designed and manufactured correctly
The pressure canners dial gauge is more accurate for adjusting for food types and altitude, as you can get exact numbers not just 10 psi and 15 psi as with typical weight regulated pressure cookers. But for low acid foods you need 15 psi anyway
Pressure preserving is done because of the higher temperatures reached. This saves time and energy, and some food react better to a short 250°F (120°C) cook that an long 210°F (100°C) cook
Pressure preserving high acid food is worth doing as long as the food does not deteriorate quicker due to the high temperature (some soft fruits will)
For preserving low acid foods you need a known good pressure cooker that can reach 15 psi (103 Pa) and therefore 250°F (120°C)
With a commercially published recipe that has been acid level tested, you will have a published time that will be safe. For a home-made recipe you have to take the worst case scenario for the acid level of the main content, and cook for that. Your local government health department will most likely publish tables for this that you should be using. Remember to use altitude adjustments for timings too
Just relying on adding a teaspoon of vinegar or lemon juice per jar is not a safe and scientific method for raising the acid level, though many people do it, and have not come to any trouble with it?
You pressure cooker should come with a manual that confirms what it can or cannot do. Download a new copy if this has been lost
Also see What kinds of pressure cookers are there, and what are they good for?
Best Answer
I don't think that device exists, its hard to say something like that.
But I can tell you for sure that this kind of device wouldn't be very efficient or useful, let's assume you are using water for cooking, if you want to boil it and cook your food at higher temperatures you would use higher pressure, for lower temperature, lower pressure, but there is no need to control it with precision since the boiling temperature shows little variation with the pressure (at 2 atm you boil water around 120ºC, at 0,5 atm it is around 80ºC), so you basically have a pot that can be ajusted for high pressure or low pressure cooking, but without precision.
A second factor to consider is the packing, to go higher than 2 atm (where a normal pressured pot gets) you would have to get a more expensive packing system to prevent your pot from exploding, so now we have a regular pressured pot with the option for low pressure.
The low pressure system wold be quite complicated to develop, since when you boil the water it turns into vapor and will raise the pressure of your pot, so you need something that will keep put vapor out of your system, something like a pump would have to be constantly working fot that to happen, that's not very practical.
And at last, I can understand why you would want to cook with higher pressure, I do it quite often myself, but I can't see a good reason to do it with low pressure, there are many cooking techniques that use vacuum, sous-vide for exemple, but I have never seen one that uses it in a sealed pot like you are proposing. You could say you want to cook in low temperatures which is completely fine, but you can do it in a less complicated way, like using an electrical heater and thermostat.
So it may exis, but as i said it would be unpractical