What causes the lights in my house to dim?

I have four-bulb fluorescent light fixtures in my house. Is it unsafe to remove some of the bulbs from each one and still use the lights with the remaining bulbs?

I recently bought a used clothes dryer. It came with a 3-prong cord, but I have a 4-prong outlet. How do I hook it up? I was told that switching the cord can be tricky.

I was shocked the other day when touching my refrigerator door. I was told that this isn’t possible. Is it? 

Yes, it is possible to receive a shock from touching any metal object that is not suitably grounded to protect against fault current which could occur within a malfunctioning piece of electrical equipment.
You should have a licensed electrician look at this problem immediately before someone is seriously hurt.

Can I use a 120 volts AC to 19.5 volts DC transformer to power an 18 volt device? Or will the extra voltage damage it?

Generally, an additional volt or so won't hurt it, but to be safe, you should check the instructions that came with the device. 
However, keep in mind that most of these adapters are only approximate, meaning an 18 volt transformer may give you an approximate floating output of 19.5 volts, so it’s possible that the transformer you want to use may be even higher.