how many amps does the charger draw? it should say a number-- something like this: "4.62A" usually near the voltage of the adapter as well. that would be a good start for making sure most relay's will work.
but i am sure that it falls below the max rating of a standard bosch automotive relay available at most auto parts stores.
terminal 85 gets connected to the ignition wire
terminal 86 gets connected to ground
terminal 30 gets connected to +12v wire
terminal 87 gets connected to laptop charger
the override switch should be wired before terminal 30, but after the fuse.
for the fuse size, go with the closest rating near to that "A" reading the charger says. i believe it will be either a 5 amp fuse, or a 10 amp fuse.