What's a 'larger power supply'?
Most store bought computers include a power supply of 250 watts to 350 watts. This is the box that converts from 110V to +12V and +5V for the motherboard.
State of the art video cards can use a lot of power just by themselves, and that extra power load can cause an existing power supply to fail.
A couple of years ago, my son needed a 550 watt PS for a home brew computer. Nowadays some systems even need a 650 watt power supply.
Top of the line systems today can have 2 GBs of memory, multiple hard drives, two DVD burners and lots of other stuff. The power needs increase very fast.