What is difference between outputs of Fourier transform and Fourier series of a periodic square waveform?
The Fourier transform $X(\omega)$ of a $T$-periodic function $x(t)$

$$ x(t+T) = x(t) \quad \quad \forall t $$

having complex Fourier coefficients $c_n$

$$ x(t) = \sum_{n=-\infty}^{\infty} c_n e^{j 2 \pi n t/T} $$

$$c_n = \frac{1}{T} \int_{0}^T x(t) e^{-j 2 \pi n t/T} \ dt \tag{1}$$

can be expressed as a weighted sum of Dirac impulses, where the weights are given by the complex Fourier coefficients:

$$X(\omega) \triangleq \mathcal{F}\left\{ x(t) \right\} = 2 \pi \sum_{n=-\infty}^{\infty} c_n \delta\left(\omega - \frac{2\pi n}{T}\right) \tag{2}$$