9 volt DC adapter with at least 850ms (0.85 amp) capabilty with the center the minus polarity.

The power jack should have a little diagram that shows the ring and tip. The ring is the long sleeve on the plug, and the center would be the tip. The diagram should show the polarity. It's usually minus to the outer sleeve (ring), and plus to the tip. It might be on the adapter spec plate also. How to tell polarity expected of DC barrel jack
The circuit board should indicate the polarity (plus and ground).

if you're using an adaptor other than the original zoom, make sure it's 300mA or more and try switching the polarity.

There is NO POLARITY to worry about since you MUST use an adapter that supplies 9 volts AC at around 850ma. You CANNOT use a DC adapter with this unit and have it work. Putting a DC adapter of 9 volts on it won't damage it, it just won't work.

AC output adapters are harder to find.

Your adapter should be a 12 volt DC delivering 2 amps (2000 ma). If the adapter is too small, you will have the symptoms you are seeing. Make sure the polarity is correct. DO NOT use the so called "universal adapters".

Easy answer: You DON'T set the polarity because this particular device takes a 9 VAC at 2.1 amp adapter. (Not a DC one like so called universal ones)
It sounds like you have one of those universal adapters which probably would not deliver the 2.1 amps required even if the lexicon took DC. Note that stuff might light up, but the unit will not work using a DC adapter..

You had better get an official power supply for this unit as what you have will NOT work, period!

I did a quick search to try and find a link to a supplier, but they are RARE !!! Every one I found would require you changing the plug to match the Lexicon.

You should just order the correct one from Lexicon.

You need a 9 volt DC adapter with at least 850ms (0.85 amp) capabilty with the center the minus polarity. A good place to find thes is thrift shops, but DO be careful that the center is the MINUS polarity.

You would be safe with a 12 volt DC adapter of 1 amp capacity.

YOU MUST match the polarity and I can't find if the center pin is positive or negative. It SHOULD be marked on the case near the plug for the power in.
Use a bright light and see if the pin or the shell is shown as + or -
Notes this is the only critical thing to get right once you have a 12 volt DC adapter that fits the jack.

You should immediately quarantine what you plugged in and compare it to the correct one.

IF you put too low aq voltage of the CORRECT polarity nothing should have happened.

If you put backwards polarity of any voltage the regulator is probably fried internally and possibly an input bypass cap. Also if you put an AC adapter and it wants a DC the same destruction could happen.

if you put too high a voltage, possibly the power input cap may be bad.

It appears that the correct supply is the PA3C which is a 12 volt, 700ma with positive on the center pin.

I believe that is the wrong VOLTAGE !!!

The PSR takes a 12 volt, 1 amp or more DC power supply with positive on the pin.

If you have connected 24 volts either AC or DC of either polarity you have likely caused internal damage. Try a 12 volt DC supply and if it doesn't work, it needs to go to a repair facility.

ALWAYS check the voltage and the polarity on ANY of the devices using the power adapters BEFORE connecting the adapter..

Check the adapter is the right voltage AND polarity for the Casio... I believe they usually take a 9 volt DC adapter with the center pin being MINUS polarity.