In my experience is hard to distinguish between different types of USB/Serial converters from product description. 99% of low cost converters claims RS232 compatibility but they have a TTL interface (0,+5v) that works only with the so-called "TTL tolerant RS232". In our case, they can be only used for the AUX interface. For all the other mount interfaces a "quasi-https://indilib.org/telescopes/celestron/celestron-aux-driver.htmltrue" USB/RS232 converter (-5,+5v swing ) is sufficient.
Below there is a copy taken from indilib.org/telescopes/celestron/celestron-aux-driver.html of the specification of each interface of Celestron scopes, including the required voltage swing.
HC: serial cable connected to hand controller serial port (less recent models).
4 pins connector (RJ11).
3 wires used: GND, TX, RX.
RS-232 serial voltage levels (+5V,-5V).
9600 baud transmission speed.
No transmission flow handshake, no echo.
Command protocol: pass through (mostly
AUX
protocol encapsulated inside HC messages).
HC: USB cable connected to hand controller USB port (most recent models) (alpha testing).
mini USB connector.
Command protocol: pass through (mostly
AUX
protocol encapsulated inside HC messages).
AUX: serial cable connected to Celestron AUX port.