Very limited number of built-in components for simulation in Altium
Altium's focus is not on simulation, but on PCB design, so the simulation library is quite limited out-of-the-box. I have never used Altium for simulation. I generally use a separate simulator (usually LTSpice) to simulate my designs before designing the PCB. It's not a one-stop shop but it gets me through. If you're really set on a combination simulation &amp; PCB design program you might consider Proteus ISIS/ARES.