If there is no relationship between the two companies—the only link is that you, the employee, work for both of them—then yes, you can make salary deferral contributions to both, up to an aggregate amount of $19,500 per year for 2020 and 2021, with no more than $13,500 to one of the SIMPLE IRAs for both 2020 and 2021.
Maximum Contributions
The maximum aggregate contribution for an individual who reaches age 50 by the end of the year is $26,000 for 2020 and 2021. An individual who participates in multiple retirement plans can defer no more than $19,500 for 2020 (regardless of the number of plans in which he or she participates) plus catch-up contributions of $6,500.
On the other hand, if the two companies are affiliated or related in any way—if there is anyone party that has ownership of both companies, whether in part or 100% ownership—or if there is any relationship that would constitute an affiliated service group, then the maximum amount that the individual can defer to both SIMPLEs may be limited to $13,500.