sovereign wealth funds derive their seed funds from interests on foreign reserves, pension funds, government budgetary surplus (government revenue is derived in large part from taxation (direct and indirect))
china has a large budgetary surplus, possibly through its position as the manufacturer of the world
uae has a large budgetary surplus, possibly through the surging oil prices
what happens if they make a bad choice?
it all depends on their primary source of funds and the urgency of needing fresh funds to replace the shortfall