If the engine requires a fuel pump for operation (always the case for fuel injected engines, and generally the case for low wing airplanes), a second fuel pump, powered by a different power source, is required for certified airplanes. Thus, engine driven pumps (obviously powered mechanically from the engine) are supplemented by (usually) an electric pump. I have observed that commonly, the type of pump will be different for each.
For my experience, the engine driven diaphragm pumps on Lycoming engines are remarkably reliable. Similarly, the electric pulse pumps (Facet brand) are really good. The electric motor fuel pumps on many of the larger Cessna singles are less than ideally reliable, and very expensive to rebuild.
Going back 75 years in design, I brought back an original DHC-2 Beaver a few weeks ago - the second fuel pump is a hand operated (wobble) pump, which you use to bring up the fuel pressure for the start, and then help along as the engine driven pump picks up the pressure. If the engine driven pump won't, you're hand pumping the rest of the flight, and I've been told that's been done a few times!