One way:

Allow: Custom
Formula: =IF(A1="X",A2<=1000,IF(A1="Y",A2<=500))

Note, this won't allow any entry if A1 is anything other than X or Y

In article ,
"Solis" wrote:

How do I add two different validations based on the condition of another
cell? (i.e. If cell A1 has a value of "X", then cell A2 cannot exceed
$1000.00, but if cell A1 has a value of "Y", then cell A2 cannot exceed
$500.00)