Question: I understand when we say current, we mean charge (protons/electrons) passing past a point per second. And the charges have energy due to the e.m.f. of the power supply.

Now tell me, if a lamp has resistance and you hook it in the circuit, how will the current stay the same? The charges obviously lose energy in the lamp and so become SLOWER, which should mean current decreases, right?

[Edit]
All answers explained a bit of everything, so it was hard to choose one. If YOU are looking for an answer, please check the others too, in case the accepted one doesn't answer your question.

Answer: 
> 
> The charges obviously lose energy in the lamp and so become SLOWER
> 
> 
> 

The charges lose potential energy, not kinetic energy. Since they're not slowing down, it's not a problem.

Imagine that I let my car drift down a mountain. The engine isn't running, but I'm in control with the brake pedal. And I'm going to make sure the car always moves at exactly 15 mph.

The car starts with some energy at the top of the mountain. As it moves, it pushes energy into the brakes. Why doesn't the car slow down? Because it's gaining exactly the same amount of energy by dropping down the mountain. The speed and kinetic energy don't change because the energy sent into the brakes is identical to the change in potential energy by moving lower down the mountain. Or you could say the force from the brakes is balanced by the force from gravity.

If the slope is steep, I press harder on the brakes and they get hotter. If the slope is gentle, I release the brakes and they cool off a bit.

In the circuit, when the charges move through the resistor, the energy lost to the resistor is balanced by the energy from the electric field. The resistor is trying to slow down the charge, but the field in the resistor is pushing them along so they keep their speed.

At the "end" of the circuit, the charges have minimal potential energy (like the car at the bottom of the mountain). The voltage source does work on the charges and moves them to the part of the circuit with the greatest potential energy.
Ok , so I think that confusion lies in the concept of current. When we apply potential difference through a circuit having resistance, a single electron does not move from one end to the other. What actually happens is that it replaces electron next to it which in turn replaces the electron next to it and this happens till the last electron reaches the other terminal. The resistance from beginning itself shows its effect on the movement of charge and not when the charge passes through it. What u say is that a charge when passing through a resistance should lose energy and hence current shoould slow down is partially correct. Yes, resistance does slow down the movement of electron but that effect is observed in overall circuit and not just in the path where resistance is connected.