Hottop's internal power regulation keeps power levels constant for small voltage variations. It is effective for power levels under 100%. To go beyond 100%, voltage can be increased with transformers. The most popular transformer used for that purpose is variac (autotransformer).
When unloaded variac is switched on to a supply, it draws large magnetizing current of order of 8–30 times the full load current, known as inrush current. When connected directly to the main, my breaker trips almost every time.
Bullet proof soft-start solution would include rotary OFF-ON-ON switch, but because I could not source reasonably priced one, I used two simple and cheap DPST switches.
Downside of the two switch solution is that I have to remember to engage switches in certain order.
1. Make sure SW2 is OFF
2. Turn SW1 ON
3. Turn SW2 ON
Advantages:
1. Breaker never trips
2. Dirty power during transient phase is not passed to the output
Bulb size is not critical. I used one I had handy, pulled out from some old appliances.
Of course, the same schematic can be used for any variac.