Can You Solder 120v Connections

From a practical standpoint, it's fine if you have proper strain relief, such as wire clamps where the wire enters the box -- but solder connections are much less forgiving of improper strain relief than other connection types. Possible, but you will want to make the wire/connector have a mechanical connection (e.g.; twisting the wire, crimping etc.) and then solder. Solder-only connections may add resistance, and therefore heat, and therefore can melt since the solder melting point is much lower than the wire itself.

Yes, a pure solder connection, where the gap between conductors is solder, may be higher resistance, because tin isn't as good a conductor as copper. But an already twisted splice, with resistance x, if soldered can only have resistance x-y. You can solder it but only AFTER you have made it mechanically and electrically connected.

The reason for this is that solder is not an especially good conductor and will generate substantial heat if current passes through the solder rather then directly from wire to wire. As others have said, no it is not ok to solder 120Vac wires directly to any kind of light bulb. Use the proper tools or don't do the project.

You could hurt yourself or someone else. Maybe you should find a friendly electrician, and ask them what they think of your idea. Main reason is safety.

Yanking out the power cable isn't as dangerous if it's a proper socket. That said, it's common to see directly wired stuff in retail products, but they use cable crimps and slack to help increase safety. I'm sure someone else can provide a much better answer, though.

Soldering is appropriate for connections that are to be permanent, where serviceability doesn't apply. More specifically, soldering is preferred for automotive/vehicular applications, and some low-voltage applications where the best results are achieved with solder. I've already cut out the back of a cheap power supply and all I need to do now is cut an AC power cable and solder it to the female plug so I can connect that to the power supply inside my chassis.

I'm not an electrician, but as far as I know it is not necessary to solder wire connections, including stranded wires, in home wiring if they're tightly twisted together and you use the proper size wirenut. I have soldering iron and a glue gun that can handle 120 VAC through 240 VAC. They seem to get away with it because the heating element has a positive temperature coefficient of resistance, and tends to keep the temperature similar with the different input voltages.