Xenon | Jasper| Valhalla
1.79A | 1.14A | 0.88A = power idle
1.43A | 0.97A | 0.73A = playing a DVD
2.17A | 1.34A | 1.14A = Grand Theft Auto IV**
1.93A | 1.24A | 1.01A = Left 4 Dead**
111 | 89 | 77 = temperature* idle
104 | 92 | 79 = playing a DVD
113 | 102 | 83 = GTA 4**
114 | 100 | 85 = L4D**
*these are all in degrees Farenheit.
**the games were not installed for these tests
So as you can see, the 360 S uses about half the power of launch model consoles, and also runs much cooler.
This is because the Valhalla combines the CPU and GPU onto a single 45nm chip versus the Xenon that had seperate 90nm chips and the Jasper that had seperate 65nm's.
Inside, the 360 S is also laid out much more efficiently, and a single fan draws in air from multiple ports and expels it through the large array of slots on the top (or side if you have the console vertical) which keeps the unit very cool inside and also much quieter than earlier models.
Installing games to your HDD will probably lower power consumption and temperature even more as the console doesn't have to spin the disc and there would be a little less heat build up.