Complex sentence: A later addition, NuBus90, bumped the clock rate to 20Mhz for better throughput and added an always-on +5v "trickle" power supply for tasks such as watching the phone line while the computer was turned off.
Split into simpler sentences: A later addition, NuBus90, bumped the clock rate to 20Mhz for better throughput. They did add an always-on +5v "trickle" power supply for tasks such as watching the phone line while the computer was turned off.