Can I use the withstanding voltage testers of TOS series as a high-voltage power supply?

No, the designed purpose of our withstanding voltage testers is the electrical safety testers.
The product specification and safety are ensured only when you use them as the testers.
If the specification conditions (e.g., the ambient temperature and output current) are met, you may think you can use them as a power supply.
However, if you use them not for their intended purpose, their normal operation or performance are not guaranteed.