inside /var/spool/cron/crontabs/root

add the following line
*/5  *    *   *   *   vim-cmd vmsvc/power.getstate 5 | grep "Powered off" && vim-cmd vmsvc/power.on 5

Useful commands:

List all VMs
vim-cmd vmsvc/getallvms

Get the power status of a particular vm
vim-cmd vmsvc/power.getstate 5

this will return ether "Powered on" or "Powered off"
eg: 
Retrieved runtime info
Powered on

(Source: https://vswitchzero.com/2021/02/17/scheduling-tasks-in-esxi-using-cron/)