使用Linq对双精度值字典列表的最简单扩展：

public static class ExtListOfDict {
    public static Dictionary<TKey, double> SumValue1<TKey>(this List<Dictionary<TKey, double>> list)        
        => list?.SelectMany(i => i).ToLookup(i => i.Key, i => i.Value).ToDictionary(i => i.Key, i => i.Sum());

}

无链接：

public static Dictionary<TKey, double> SumValue2<TKey>(this List<Dictionary<TKey, double>> list) {
    if(list?.Count > 0) {
        var dir = new Dictionary<TKey, double>(list[0]);
        for(var i = 1; i < list.Count; i++) 
            foreach (var kv in list[i])
                if (dir.TryGetValue(kv.Key, out double sum))
                    dir[kv.Key] = sum + kv.Value; 
                else 
                    dir.Add(kv.Key, kv.Value);                    
        return dir;
    } else
        return null;
}

如果您喜欢LINQ方法，我会选择类似以下的方法：

var dictionaries = new List<Dictionary<string, int>>(); // this is the list of dictionaries you want to merge
    var unifiedDictionary = new Dictionary<string, int>(); // this is the dictionary where you merge and add the values

    foreach (var kvp in dictionaries.SelectMany(dictionary => dictionary))
    {
        if (unifiedDictionary.ContainsKey(kvp.Key))
        {
            unifiedDictionary[kvp.Key] += kvp.Value;
        }
        else
        {
            unifiedDictionary.Add(kvp.Key, kvp.Value);
        }
    }

但是，如果这太难阅读（我并不总是喜欢在显式代码块上使用过多的LINQ），您可以使用for-loop方法：

var dictionaries = new List<Dictionary<string, int>>(); // this is the list of dictionaries you want to merge
    var unifiedDictionary = new Dictionary<string, int>(); // this is the dictionary where you merge and add the values

    foreach (var dictionary in dictionaries)
    {
        foreach (var kvp in dictionary)
        {
            if (unifiedDictionary.ContainsKey(kvp.Key))
            {
                unifiedDictionary[kvp.Key] += kvp.Value;
            }
            else
            {
                unifiedDictionary.Add(kvp.Key, kvp.Value);
            }
        }
    }

希望这对你有帮助。如果需要进一步的帮助和解释，请告诉我。

下面是一个基于CollectionsMarshal.GetValueRefOrAddDefault API（.NET 6）和INumber<TSelf>接口（.NET 7）的解决方案：

public static Dictionary<TKey, TValue> ToSumDictionary<TKey, TValue>(
    this IEnumerable<Dictionary<TKey, TValue>> dictionaries)
    where TValue : struct, INumber<TValue>
{
    ArgumentNullException.ThrowIfNull(dictionaries);
    Dictionary<TKey, TValue> result = null;
    foreach (var dictionary in dictionaries)
    {
        if (result is null)
        {
            result = new(dictionary, dictionary.Comparer);
            continue;
        }
        if (!ReferenceEquals(dictionary.Comparer, result.Comparer))
            throw new InvalidOperationException("Incompatible comparers.");
        foreach (var (key, value) in dictionary)
        {
            ref TValue refValue = ref CollectionsMarshal
                .GetValueRefOrAddDefault(result, key, out bool exists);
            refValue = exists ? refValue + value : value;
        }
    }
    result ??= new();
    return result;
}

每个字典中每个KeyValuePair<TKey, TValue>的键只散列一次。

如果您因为重复的键而得到异常，那么听起来就像您有重复的键！
在尝试合并两个字典之前，您是否检查过它们？简单地调用=+ kvp.value，而不检查第一个字典是否已经有该名称的键，这很可能是您的问题。
您需要检查具有该键的现有条目，如果找到，则采取适合您的场景的任何操作（即忽略、覆盖、要求用户决定等）