t, Sql Server - rextester

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CREATE TABLE LinkStockEquipment
    ([Stock ID] varchar(2), [Equipment ID] varchar(2), [Equipment Qty] int)
;
    
INSERT INTO LinkStockEquipment
    ([Stock ID], [Equipment ID], [Equipment Qty])
VALUES
    ('A1', 'E1', 5),
    ('A1', 'E2', 3),
    ('A2', 'E3', 4),
    ('A2', 'E4', 6),
    ('A3', 'E5', 2)
;

SELECT 
     [Stock ID],
     [label],
     [Value]
INTO tmpResult
FROM (
    SELECT 
         [Stock ID],
         'Eqp ID ' + CAST(rn AS VARCHAR(16)) as label,
         [Equipment ID] as [Value]
    FROM ( SELECT *, row_number() over (partition by [Stock ID] ORDER BY [Equipment ID]) as rn
           FROM LinkStockEquipment ) as rows
    
    UNION ALL
    
    SELECT 
         [Stock ID],
         'Eqp Qty ' + CAST(rn AS VARCHAR(16)) as label,
         CAST([Equipment Qty] AS VARCHAR(16))  as [Value]
    FROM ( SELECT *, row_number() over (partition by [Stock ID] ORDER BY [Equipment ID]) as rn
           FROM LinkStockEquipment ) as rows
    ) as x;

SELECT * FROM tmpResult;

DECLARE @cols AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX);
    
SET @cols = STUFF((SELECT distinct ',' + QUOTENAME(c.label)
            FROM tmpResult c
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'');
        
SELECT @cols;

set @query = 'SELECT [Stock ID], ' + @cols + ' FROM  
            (
                SELECT *
                FROM tmpResult
           ) x
            pivot 
            (
                 max(Value)
                for label in (' + @cols + ')
            ) p '
                
execute(@query)

View schema
Execution time: 0,03 sec, rows selected: 16, rows affected: 5, absolute service time: 0,25 sec, absolute service time: 0,24 sec