I know that 2 25A rail = 1 50A but what computer parts use the 12V rail and will I have to get an adapter or something?
Not necessarily. A psu will have a maximum output that is often less than the sum of the rails. One needs to check the data plate specs.
The +12v rails is used for primarily the cpu, graphics cards and peripherals. That is almost all of the power output.
Some cheap psu's advertise high wattage, sending much to the 3.3 and 5v outputs.
Really single/multiple rails is a non issue. In theory, multiple rails limit the current to a single section of the psu for safety reasons.
In actuality, a quality psu has no safety issues regardless of how many rails it was designed with.
And, no, you need no adapters.
Just check how many power leads your components require. If the psu has sufficient, odds are, that it also has sufficient power to do the job.