Source: Superman vol.2 #123 (1997) to #135 (1998)
Type: The real dealWelcome to Electric Superman Week!
In the late 90s, the Super-books needed a stunt to boost their sales and since Superman had died in relatively recent memory, well, they decided to change his look and powers for a while. It's something readers were eager to forget about judging by how much play it has on the Internet today (as in, very little), but we're gonna stick with it for a whole week!
Wait! Come back!
Now, I wish I could tell you definitely how Superman became an out-of-phase energy being overnight, but it was never really explained. My guess is that his powers got wonky after Final Night in which he plunged into the sun. Some theories say it's because he traveled to an out-of-phase Kandor City. Others lay it at the feet of the New Gods. Whatever truly happened (and the road back wasn't any clearer), we now had a Superman with energy powers, and who had to wear a special containment suit built by Professors Emil Hamilton and "Rampage" Faulkner to live normally. He could change into Clark Kent, but Kent had no powers. Well, Superman seemed to enjoy the change, at any rate.
This lasted, in one form or another (more through the week!), for X months, across all the Superman titles and JLA for about a year, which was at the time my only exposure to it. Though Grant Morrison was more than equal to the task of giving this Superman cool shticks, it seemed a shame that the new "all-classic characters" JLA was stuck with a non-classic Superman.
Not that they'd ever change Superman's paradigm for a whole year these days. Cough.
Where were YOU when Superman went electric? (Yeah, I know it's not exactly Man's first walk on the moon.)