It's not equivalent. It connects to the hots on 2 circuits. It then connects (shorts if you like) the 2 grounds on the 2 circuits. It also connects the 2 neutrals on the 2 circuits. You may get 2 120V legs with no 240V or you may get 2 120V circuits with 240V. If a house was wired this way it would be in violation of codes for good reasons. It is now possible to overload the common ground or the common neutral because a parallel circuit has been created.
Some CGs will not allow the cheater cord as it's known.
I'll look and see if I can find some some of my prior posted knowledge on this subject.