Transformerless Power Suppply

[T.Jackson]

Short answer is because it's much safer. But there are also other advantages
as I will spell out here...

1. Cleaner power, typically around 5mVPP of ripple - (AC component) - with the usage of sufficiently sized reservoir caps. General rule of thumb: 10uF for every 5mA of current. So, at 1 Amp you want at least 2200uF.

2. Well designed transformers are extremely efficient. Typically 95% or better.

3. Power transformers are reasonably immune to interference.

4. Isolation transformers are critical for the novice for when it comes to taking
high voltage measurements on an oscilloscope. In fact, no one should really take measurements without using it.

Trent Jackson