C++ doesn't support template specialisation based on typedefs, so wrap a float in a struct.

gistfile1.cpp

#include <iostream>
using namespace std;

struct Float
{
    Float( float val ) : m_val( val ) {}

    operator float() { return m_val; }

    float m_val;
};

#define DeclareFloatType( name ) \
    struct name : public Float \
    { \
        name( float val ) : Float( val ) {} \
    }

DeclareFloatType( ReactivePower );
DeclareFloatType( RealPower );

ReactivePower raps[10] = {1,2, 3, 4, 5, 6, 7, 8, 9, 10};
RealPower rps[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

template <class T>
float getPower( T* items )
{
    return 0;
}

template<>
float getPower( RealPower* items )
{
    float val = 0;
    for( int i = 0; i < 10; i++ )
    {
        val += items[i];
    }

    return val;
}

template<>
float getPower( ReactivePower* items )
{
    float val = 0;
    for( int i = 0; i < 10; i++ )
    {
        val += 2 * items[i];
    }

    return val;
}

int main( int argc, char **argv )
{
    cout << getPower( rps ) << " " << getPower( raps ) << endl;
}