suppose in a "No Limit Holdem"

player A bets 100,
player B raises to 200 (100+100) and
player C goes all in for 250 (not a full raise).
If player D wants to raise (by 100) he
must raise to 300 (200+100) or to 350 (250+100)?

i believe it is 350

3. All raises must be equal to or greater than the size of the previous bet or raise on that betting round, except for an all-in wager. Example: Player A bets 100 and player B raises to 200. Player C wishing to raise must raise at least 100 more, making the total bet at least 300. A player who has already checked or called may not subsequently raise an all-in bet that is less than the full size of the last bet or raise.

That's from Robert's. It says except for an all in wager, making me think 300 is legit, but that's an interesting scenario and it would be interesting to know if there is any variation in how different poker rooms handle it.