With switching power supplies you need a big capacitor to help out. Are you sure that coil is a 48V coil? Most 48V coils are 4+ ohms. Even then though, it'll only be drawing that much for maybe 50ms. As long as your transistor can handle it the capacitor should tide it over

Pinball solenoids draw a lot of power but it's supposed to be momentary, which is why it's a big issue when a coil locks on. So since at a minimum with 48V and 4 ohms the solenoid is gonna draw 12A, your power supply can't power it straight up. However, Zacaj is right, the solution is to use a capacitor that can power the solenoid instead. So using a couple formulas from here https://sparks.gogo.co.nz/capacitor-formulae.html , the minimum capacitor size you're gonna need to provide 12A for 50ms is around 1300uF, but realistically you'll want to go larger, probably around 3-5000uF. The basic circuit should look something like this http://tinyurl.com/y6o25don

I'd just throw a 15000uF on there and be done with it. Never know if two coils might be firing at once or anything

Yea always better to have too big of a capacitor with something like this.