R1=100;
C1=(10^(-4));
f=50;
us[t_]:=100*Sin[2*π*f*t+π/2];

eq=((us[t]-uc[t])/(R1*C1))==uc'[t]

eqInit=uc[0]==100;

ucRes=uc/.NDSolve[{eq,eqInit},uc,{t,0,0.2}][[1]]

a+1/.{a->b}

plND=Plot[ucRes[t],{t,0,0.2}]

R1*C1//N

tmax=0.2;
Δt=(1/f)/20.;
stepEuler[{t_,uc_}]:={t+Δt,uc+Δt*((us[t]-uc)/(R1*C1))}

NestList[stepEuler,{0,100},Round[tmax/Δt]];
plEu=ListPlot[%,PlotStyle->Red];

Show[plND,plEu]