It’s very easy to exceed 250+ watts on old CPUs like x58 hexacores, new ones seem to limit themselves internally. A quick look at a review shows 3950x pulls a little more power than a stock x5690 which has a stock tdp of 130w, where the 3950x was doing all core boost at 140w. Pretty energy efficient.
3770K @ 4700 1.375v|Le Grand Macho RT/TY-143|Asus P8Z77-V|8GB G.Skill Mix @ 1100 9-11-9-28 2T 1.68v|Intel 545S @ Raid 0|EVGA GTX 980 Classified @ 1500/2001|CM Silent Pro M2 850|FD Meshify C TG
X5690 E.S. @ Stock+Turbo|True Spirit 140 Power/TY147B|Asus Rampage III Formula|10GB G.Skill Mix @ 666 8-8-8-24 1T 1.575v|Intel 520|EVGA GTX 970 FTW ACX 2.0 @ 1404/1753|TT TP650|FD Define R4