You need to match the transformer to the bell or chime, not to the switch. Most doorbells are 24Volts, but some require a bit more current than others.

Most door chimes are 16 volts. Older (much older) chimes might be 10 volts.

What are you planning to use this for? It's not a doorbell switch. Is it for an alarm system, or just a visitor announce thing?

Keep in mind if you plan to connect a doorbell to that switch unmodified, it may overheat. Most are not rated for constant use, but as long as the door is open, a "dingdong" doorbell will be energised. You'll hear "ding" but no "dong" until the door closes.

I learned this the hard way, it melted the doorbell a bit. My solution was to connect the bell to a relay, on the normally closed terminals. When the circuit was energised, the relay would open so the chime was really a pulse- very quick, but it was perfect.