I have a vintage leviton switch. you plug it in a 200 or a 125 watt receptacle and it has several outlets on the side where you plug in another electrical appliance, iron, radio, etc.. how old is this receptacle and what is it worth

Your description doesn't explain the circuit, the function of the wires or how the switch controls the outlet and whether the switch is a single pole or two-pole switch. Without such details it is difficult to visualise the circuit.

I advise before you go further to test the sensor in a known good and correctly wired outlet using a length of cable and a suitable plug for the outlet. It is possible the unit is faulty. If it functions correctly on test you will need to understand the circuit and the function of the wires before you rewire it to assure success.

Wait... you cannot replace light switch with outlet receptacle.
You have to test wires first.... then Hot wire connects to brass screw on receptacle,,,, and neutral wire connects to silver screw ( ground to green screw) ... you got several important details right, but you have to identify hot and neutral wires first.
Read instructions:
http://waterheatertimer.org/Basic-house-wiring.html#test

http://waterheatertimer.org/How-to-add-outlet.html

Gene

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Copy following links:
http://waterheatertimer.org/How-to-wire-combination-switch-outlet.html
http://waterheatertimer.org/images/Combination-switch-outlet-6.jpg

Gene
h

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

On one side you will have one brass screw and one silver screw. Connect the hot wire (usually black) to the brass screw and the neutral (white) wire to the silver screw. That's it, it comes from the factory ready to switch the outlet.

Any off-the-shelf GFCI sold today with work on 12-2 wire:
By code, 12-2 wire should be connected to 20 amp circuit breaker, but typically most switches and outlets wired to that circuit are rated 15 amp. Amp rating is printed on electrical devices.
Leviton 15 amp 7599-W:
http://www.amazon.com/Leviton-7599-W-Receptacle-Feed-Through-SmartlockPro/dp/B000VYO9MU/ref=pd_cp_hi_3
Leviton 20 amp 7899-W
http://www.amazon.com/Leviton-7899-W-SmartlockPro-Indicator-Wallplate/dp/B000N663PM/ref=pd_cp_hi_0
Wiring:
http://waterheatertimer.org/How-to-wire-GFCI.html

Leviton T5625 has shutter (tamper resistant) mechanism that blocks access to the contacts unless a two-prong plug is inserted. My understanding is this mechanism prevents child from sticking piece of metal into receptacle and getting shocked. Tamper resistant receptacles are code for new home construction, and receptacle is marked with TR. The light switch part of device works at all times, with or without two-prong plug in receptacle.
http://www.leviton.com/OA_HTML/ibeCCtpItmDspRte.jsp?item=388754§ion=24614&minisite=10026

Electricians test, they don't guess.

Let's test your wires using ordinary two-prong tester.
Tape wood sticks to tester leads to keep hands away from power. Stand on dry surface or wood boards. Do not shake or sweat.
Separate wires for testing
Turn power ON.
Test each wire to bare ground wire.
Tester lights up on Hot wire. Hot wire connects to either dark-colored screw, as long as there is a brass connector plate that connects both dark colored screws. If connector plate is missing, add a jumper wire between both dark screws so they are connected together.
Hot wire is identified.
Now test Hot wire to each other wire, except bare ground wire.
Tester lights up on neutral wire. Neutral wire connects to silver screw.
If neutral wire is white wire, AND both white wires were connected together before, then they both connect to silver screw.
The last wire is the Load wire that goes to fan, light, motor. Load wire connects to brass colored screw.
Double check instructions with instructions on new device.
Add a comment any time.

You can also take advantage of fixya phone service.
For a price, fixya expert speaks to you over the phone while you test and wire the device.

Assuming you have a tie on only one side, you should not use either screw on that side of the unit. Connect your hot wire to the screw on the other side of the unit on the end closest to the switch. This should be an isolated brass screw. This will allow the hot wire to feed through the switch, then through the hot tie to the outlet end of the unit. Connect the white neutral wire to the other screw on the same side that you connected the hot wire. This should be an isolated silver screw toward the outlet end of the unit. Connect your ground wire to the ground terminal. good luck Al K

For what you want to do, the side of the device that has the two brass screws tied together with a metal break off tab is _not_ used, and do not break off the tab ("tie") On the other side of the device, connect the white (neutral) wire to the silver screw and the black hot wire to the brass screw that is just above the silver screw on that same side.

For this combo , the white wires connect to the two silver screws on one side of the combo .The black power wire connects to the screw next to the switch. IF you want to have the receptacle hot all the time then jumper the hot black from the switch screw to the receptacle screw. The screw in the center is for the black wire from any lihghts that you want to control. IF it is the receptacle that you wish to control with this switch .. then the power connects to the screw next to the switch and the center screw jump a wire to the screw next to the receptacle

You cannot replace the switch with a switch/receptacle combo because there is no neutral wire. The black and white that you see are both used as hot wires. One is the Line and the other is the Load.

You have to install another 2 wire cable or replace the existing with a 3-wire cable. A 3-wire cable has a black, red, and white, plus the bare ground wire