The original playstation was one of the systems that many different emulators tried to fully emulate. It was quite interesting coming from the 16bit era on to the 32bit with full 3d capabilities in terms of emulation coding challenges. Performance and compatibility was all over the place for many years with emulators like PSEmu, PCSX and ePSXe as well as commercial emulators like Bleem! and VGS.
The plugin system was also a way to split the workload of emulating the different subsystems of the playstation.
Fast forward many years and we have Duckstation coming into the scene as a breath of fresh air for the PSX emulation.
I must say I was so impressed with how the project approached diversity of features as well as keeping compatibility in check.
Just try playing early PSX games like Wipeout 2097 (or XL in the US) and enable the sub pixel precision with 720p resolution or higher.
It could convince you that you are actually playing a PS2 title!
Duckstation Official site