Inspired by the discussion generated by those early ads for additional conveniece outlets, I dragged out some examples from my collection.  Let's start with the lamp socket ones.  Here are a few that would have allowed one to light a bulb and screw in the plug for a toaster or coffee perk.

I will bet that some clever soul soon figured out how to add another twin adapter to the empty socket of the adapter already in place...

I've included samples of a couple of adapters that allow any two-prong plug to be plugged into a light socket.  Surprisingly, these still exist today.

Last 2 photos are the guts of the screw-in type plug. As a brat, I was fascinated by the way these would allow the cord to be connected without twisting.   Ok, still am...

The light fixture was likely the only electrical wiring in some very old kitchens and since there are never enough outlets, some clever manufacturers made these drop cord extensions.

This one was still in its box with instructions on how to wire it so that the switch would control the light while the outlets were on all the time.

I will guess it was assumed most people had a notion of basic electricity!

No surprise from me that these are all GE products...

First is a sample of one of the early duplex outlets - I am guessing from the 20s

Second is from the mid-50s. Despite the lack of wiring and poor physical placement, the house where I grew up had these all through the house!  I have seen in catalogues from the early 60s a version that could take 5 flat plugs.

Third is a GE quad outlet. These were around from the early 60s right into the 70s. Not sure exactly when they disappeared.

In the last picture, and it is not clear, the rear plate of the GE triple outlet has instructions on how to snap off a section of the cover plate to permit 2 (or maybe more!) of these outlets to be 'ganged' together.  A 9 outlet unit is what every 50s kitchen needed, no??

Now the era of living dangerously begins...

The early multiple-outlet strips like this mid-50s version of the Tap-a-Line appeared on hardware and department store shelves.

Of course if anyone bothered to read the product leaflet, these models made it pretty clear that the total power consumed was the limit to how many things could be used simultaneously.  But the temptation to use one's toaster, iron, and coffee pot must have been too great... LOL 

8 seemed to become the 'magic number' of plugs...

In the late 50s, Fedtro made these extension strips.

Again, 8 was the magic number, but if you tried real hard, you could jam in 10 or 12...

I would dispute that 15 amp rating too.

These are the ones that I remember best. They were everywhere in our house!

Fedtro 'offshored' production to Japan when these multiple outlet strips were in production. They were around for a long time, only fading in the mid 70s.

There was some fine print as to wattage capacity, but 'if that smiling model on the package can run an iron and a frypan off this, then why can't I' was the customer's attitude. Full disclosure - when one of these beasties failed it was either the attachment plug or when the solder holding the wires to the internal brass strips melted.  Not pretty...

I suppose the Hex-O-Let was the safest. Well, as safe as using 2 cube taps in a double outlet.  LOL 

But the package graphics were great and you could choose just how many extra outlets you needed...

I'll end with what could have really been Fedtro's 'safest' outlet strip.  The Benchmaster was huge, with grounded outlets AND a fuse.  Where's the fun in that??? 

I was using one of those lamp socket splitters (similar to pictures 3 and 4) at the top of the basement stairs in the pantry area of our previous house.  It had a utilitarian porcelain bare bulb fixture.  I would go in and out of there a lot, and would have to drop what I was doing if the bulb failed.  The antique splitter in a box of old wire and cords held the answer, so instead of a singe 100w bulb I had two 60s.  It's still there.  The new owners haven't begun any remodeling yet.