In article , HA HA Budys
Here wrote:
Check that your 2 new replacement bulbs aren't the newer 120 volt variety.
These "puck lights" have gone to line voltage now.

If it is you're causing a direct short by using a 120v bulb in a 12v
transformer.

I have yet to see a 20W 120V, but if there is one, it would not short
out nor overload the supply, but just run very dim. It is use of lower
voltage (higher current) bulbs on higher voltage supplies that causes
problems.

They're very pretty when lit, unfortunately, both varieties (12 & 120v) don't
have a good long bulb life. I recommend replacing the bulbs with 10 watt bulbs
of the 12v variety, they seem to last a lot longer and don't put out noticably
less light.

10 watt normally produces 150 lumens.
20 watt normally produces 350 lumens.

If the 10 watt is almost as bright as the 20 watt, then the 20 watt is
loading the voltage down or is a junky off-brand one.
Are your failed bulbs showing a smoky appearance that indicates a sign
of air leaking in? Possible causes: Bad bulb, bulb overheating due to
poor fixture design, bulb contaminated by ash, salt or alkali is cracking
(these materials leach into quartz if the quartz is hot enough, causing
weak spots and stresses in the quartz).

- Don Klipstein )