Older power bricks made for previous chipsets are compatable with the newer chipsets, newer powerbricks won't work on older systems because of the connectors for all of the new powersupplies will only allow the powerbrick to plug into the chipset it was made for or chipsets made after it.

The 360 will only draw the power it needs anyway so using a powersupply with a higher wattage doesn't hurt.

If you want the EXACT power supply that was made for YOUR xbox then I will make it easy, check the back of your 360 where you serial number is. On the bottom left of that sticker you will see something one of these lines, if your 360 matches any of the information that I post then that is the power supply you need.

12v-16.5A = You need a 203W power supply

12v-14.2A = You need a 175W power supply, but a 203 watt will work.

12v-12.1A = You need a 150W power supply, but a 175 watt and a 203 watt power supply will work.