South Australian Premier Jay Weatherill says Prime Minister Malcolm Turnbull has delivered a "very poor NBN outcome" as he unveiled plans to substantially increase internet speeds for public schools across the state through an investment worth "tens of millions".

Mr Weatherill also took a swipe on Sunday at SA Best leader Nick Xenophon, who now has 26 candidates ready to run in the state's 47 lower house seats, for siding with Mr Turnbull at a federal level to strip up to $210 million in educating funding from the state.