Electronic – Why does it hase a power supply for the rs232 to rs422

An EIA-485 ("RS" refers to "Recommended Standard", and is an obsolete name) interface is rare on a PC, you'll need a separate interface board for that. The reason is that EIA-232 and EIA-485 are not hardware compatible, despite using the same connector type: EIA-232 uses single-ended signals, meaning that RxD and TxD are referenced to ground. EIA-485 uses balanced signals, meaning that both sent and received data have a positive and negative signal which are each other's negative.

A design I have used for a while now and that seems to work very well, is to use TI ISO7221A for UART (TTL) isolation, and then a driver on the nonisolated side, i.e. MCU->ISO7221->driver. I use this with an FTDI FT231 virtual serial driver, but if you prefer bare RS232 you can just use a MAX3232 instead.

The advantage of this design is that it is a fair bit cheaper than using one of your isolated drivers, while still getting well-defined performance (contrary to using a bare photoisolator).

For isolated power I default to those SIP 5V to 5V isolated supplies, e.g. XP Power or TracoPower TMA0505S. Make sure you filter these puppies really well - at least a big (>100µF) bulk electrolytic capacitor, but preferably a full common-mode filter (CM choke + 2 capacitors). Unfiltered these little power supplies kick out horrible amounts of EMI.

As ESD protection I usually just stick with simple BAT54S clamping to the ground and Vcc: cheap and cheerful. Make sure to put a nice big zener on the power lines as well, as close to possible ESD sources and clamping diodes as possible, with nice fat traces.