Current draw on 12 volt power supply
If you switch to LED light's with the same brightness level, they will draw only about 12% of the power of incandescent lights. They must be rated for 12 volt operation, as this would be a typical low-voltage-lighting (LVL) circuit. The power supply is most likely a transformer or switching supply powered from 120VAC. Its limit is 250amps of total current draw from all lights. The high current assumed use of incandescent or halogen lamps, because at just 12 volts you needed 10 amps per light for 120 watts of light. With 12 volt LED lamps the supply will put out much fewer amps, allowing you to install more LED lights if you want. When you choose LED lamps, make sure they are rated for 12 volts AC or DC, and check the current consumption of  each light. LED's cost more, but save lots of power and do not get hot like incandescent or halogen lamps, and can last 20 to 50 years or more. Be sure to read the fine details before buying them.