I have acquired "white belgian candi sugar" from BrewFerm, and it is in rock form. AFAIK, this is just solid invert sugar, and should have potential 46 PPG, but BrewSmith and Brewer's Friend both list them with 38 PPG. Is this correct?
There is no reason it should be different from any other sugar. I use 45 ppg and get the gravities I expect, so I would have to say that 46 is closer than 38. I suppose it could vary by brand if one brand somehow cut the sugar with something else, but I'm not aware of that actually happening. BTW, candi sugar rocks are a waste of money. Belgian brewers don't use it. They use either candi syrup or plain beet or cane sugar (like table sugar).