Still thinking about the interesting question! ***Not an answer***, but too big for a comment. To show what I meant in my comment to Daniel Litt's answer about the difference between uniform *absolute* convergence and ordinary uniform convergence: I **think** (but it was a while ago when I thought about it) that there exist $u_0, u_1, \ldots$ such that $\sum_{n=0}^\infty u_n z^n$ converges uniformly on the set $\{ z \in \mathbb{C} : |z| \leq 1 \}$, but not uniformly absolutely. Thus $\sum_{n=0}^\infty |u_n| = +\infty$, but also $$ \forall \, \epsilon>0, \quad \exists \, N(\epsilon)>0 \quad \text{such that}: \quad \forall \, |z| \leq 1, \quad \forall \, m \geq n > N(\epsilon), \quad \left| \sum_{k=n}^{m} u_k z^k \right| < \epsilon. $$ This function $f(z) = \sum_{n=0}^\infty u_n z^n$ satisfies $$ f \in A(D) \setminus W_+(D), $$ which shows in particular that the *disc algebra* $A(D)$, consisting of functions continuous on the closed unit disc and analytic on the open unit disc, is **strictly larger** than the *Wiener algebra* $W_+(D)$ of power series absolutely convergent on the closed unit disc. So the problem is going to be pretty hard because we can't use **absolute** convergence (unless I'm being stupid or there is a clever trick exploiting the special structure of the exponential functions). The easiest "solution" is just to ignore it (i.e. ***assume*** absolute convergence!) This gives a slightly different, but still interesting, question.