I think this is to avoid the plentiful 12v adapters that use those sizes, as you could fry the board with a bad PSU. The 5v adapters that do use those more stan

I think this is to avoid the plentiful 12v adapters that use those sizes, as you could fry the board with a bad PSU. The 5v adapters that do use those more standard sizes are generally 500mA or 1A, which is enough to (unreliably) boot and run the board.