In the scene reintroducing Alpha in Once A Ranger, Alpha implies he hadn't been in working order for a while. Who's been working on him to get him up and running? Adam, who had experience with Morphin' era tech, and Andrew Hartford. Who created an Artificial Human. Who better?
The Morphin' Grid is some sort of energy formed from the battle between good and evil, and the run-off energy tends to form in explosions. With multiple bad guys (and later in the team-up episodes, multiple good guys), the Grid must've been overloaded and gone crazy with the explosions.
The seemingly fridge-logical aspect of Andrew making his robot son a young adult in appearance shifts to brilliance because when he finally dies, Mack can live on his own and not be discovered by an adoptive parent.
Since Mack is a robot, he won't age like those around him. If Andrew had died before telling him who he really was, Mack would never know why this was happening. Not every day you see a teenager filling up the fridge like this...