There is a market with all kinds of amplifier types. People play guitar or bass, and people simply want more audio power, some want tube amps and the many car owners who want to upgrade their audio. Maybe the most common amplifier type are stereo amplifiers even though most people don't care so much about it. They have their cheap equipment and only a few look for better equipment whether it be new, old or vintage.
Some guys like to build on their own and one way to go is to start with a simple amplifier kit, some cables, potentiometers, knobs and an enclosure. Maybe some leds too. Making an own amplifier, can be quite fun. And inexpensive. At a young age, it can be part of a way to further knowledge.
So, generally when amplifiers are talked about we relate to manufacturers like Pioneer, Sony, Kenwood, Onkyo, Sansui, JVC, Nad or McIntosh.
Until a decade ago, separate amplifiers were common in stereo systems but in recent times with smaller electronics, the size of many units have got smaller, because of less awareness and interest for audio quality. Many stereos of today are housed in plastics and with smaller sizes, there is not power enough. But old equipment is always available almost everywhere. Many people have old gear that they do not use so it shouldn't be too hard to find even some of the vintage style with the cool blue light such as in the tuners from the early 70s.
As we see, Mcintosh also likes blue light but overall, vintage design is hard to beat, as seen on the Kenwood tuner and amplifier.
Although the computer era has kind of computerized a lot of the music playing and recording, people do play for "real" and for that purpose, instrument amplifiers are needed. mostly for guitar and bass.
Even though amplification usually starts with very low levels, most people probably think of more effect when amplifiers come to mind.
And power amplification is done in radio transmitters, or so called transceivers. Therein, he transistor that draws most current, and therefore delivers most power, as in a cb radio, is the final RF transistor that amplifies the radio signal to the antenna.
Around 1980 I had a cb radio like the one to the right. I know I damaged the transistor a couple of times, as seen below, a 2SC756. However I knew a company who had theses transistors in their surplus supply.
I remember one night, I was 14 or 15 then, I talked to a guy in Italy, I´m sure it was for an hour or so or even more. But he could hardly no english, and I could no italian. Yet we tried to talk, some words are identical between the languages anyway so I guess we performed some form of talk anyway. Those were the days.
A video amplifier is most of times just the name of a section in the electronics, where video signals are amolified and/or processed.
Either with transistors or integrated circuits.
Some amplifier types use more power, like PA amplifiers that need to provide more effects to the speakers in a live environment. Transmitters for broadcasting and tv may also use a lot of power.