On Thursday, February 26, 2015 at 1:49:12 AM UTC-5, wrote:
I have a flat screen LCD computer monitor which needs a transformer for
power. I dont have this transformer. I can get one on ebay for around
$15, but before I spend the money, I want to make sure the monitor
works. It needs 24 volts at 1.2 Amps DC. I have one from an old Laptop
computer that has an output of 16 volts 3.6 Amps DC. The amperage is
fine, but the voltage is 8 volts low. The power plug (to monitor) is
the same as needed.

I just want to be sure the monitor powers up and operate it for a
minute. Is there any chance of damaging the monitor or transformer of I
connect it to the monitor? Or will it even power it up?

If the polarity is correct, it definitely won't harm the "transformer", and I don't see how the monitor would be damaged either. I've repaired thousands of monitors with bad caps, and the resulting low voltage *and* ripple never bothered the monitors. I don't know if your monitor will start 8 volts low, and my guess is that it won't, but try it anyway.