Wattage is also the consumption, not just brightness. but you are right in the fire up and running consumption. But they don't DRAW more power to fire up,that would blow the fuse. What the ballast does, gives the lights a full charge, to they are at full power all the time. HID bulbs do not like to be run on anything less than a full charge, it kill their longevity, down to a few months in some cases.

So the ballasts "should" consume 35w, but they might just send 35w to the bulb.. You would need to meter to verify. But in that case, they would use less power than the oem.