I came across one of them flat ceiling lights, leds, 12W and mains voltage. No circuitry whatsoever. 2 strips of leds series'ed together.
I didn't read the label properly and tried to feed it usual 12v, but apparently i need mains to run it.
I have saved up loads of old tv and monitor led strips i could reuse but i need a high voltage low amp power supply of some kind, that goes all the way to 50V-240V. Is there such a thing that can be cheaply bought ? Its mostly for testing purposes, leds, small mains motors i might undervolt, no big loads etc.

Later checked another flat light panel i have been using for a while, its been fed 36V from an external brick, so its not the same thing but made me try to light the small one by 12v...

 

What makes you think devices take a "usual 12V"? Device take what they are designed for.

 

Usual (for me) in a sense that i work with 5-12v led strips/panels.

 

Before you plug them into anything else, KNOW what the specs are by contacting the seller or manufacturer. To do otherwise could be very bad.

 

Allow 3V per led. See if they are in series or parallel, then work of the voltage.

 

As @Ian0 points out, if you inspect how the LEDs are arranged, that is, are the wired in series or in series groups connected in parallel, you can calculate the voltage requirements for the strip or panel, you don't have to guess.

Photos showing the wiring would help us to work it out and show you how to do it yourself.

 

If there are a lot in series, and you need a lower voltage, a cut track and two lengths of enamelled wire and they can soon be half the voltage at twice the current!

 

If there are a lot in series, and you need a lower voltage, a cut track and two lengths of enamelled wire and they can soon be half the voltage at twice the current!

Half the total Forward voltage of the series. And the user must figure out a way to knock down the supply voltage to insure the string of series-connected LEDs is not supplied with too high of a voltage

also the comment that I will take twice the current is only true if both of the newly-created halves of the series connected LEDs are then connected in parallel and each current-limited.