More or less compared to the GTX 1070? That's hard to say.
Currently the Titan Volta is rated at a 250W TDP. This is the same as the current Titan Xp, although the Volta is the more powerful video card.
If I were to guess, the Volta cards will consume either the same, or somewhat less, power than their 10xx equivalents, while providing greater performance.
However, that is only a guess. It's impossible to know for certain. That said, I think going with the 550w power supply gives you enough room for future upgrades probably to go to a video card of somewhere in the low 200s watt range of TDP rating, MAYBE 250w or so, but that depends on the components of the rest of your system. Example: If you are running many fans, multiple...