Well if you're talking about an actual tube rectifier, then it supposedly does have some effect on the tone. Like a smoother sustain or something along those lines. I am simply mirroring information here, because I've never witnessed this myself.
Tubes operate on high voltage DC. At the power input of an amp, there is a transformer that steps up 60 Hz 110 VAC to several hundred VAC @ 60 Hz. That is followed by a rectifier circuit which converts the several hundred VAC to DC. This DC high voltage is then distributed to the tubes which modulate the DC back to AC, but at the frequencies of the input signal.
Believe it or not, a couple good bits of info in there.
To add, the tube rectifier is supposed to impart a tonal quality when the audio tubes are driven hard. As the audio tubes are driven harder, the power supply (Rectifiers) can keep up with the instantaneous demand...the power supply voltages sag just bit which well softens the audio output.
Solid state rectifiers don't exhibit this nearly as much. Switch the amp to solid state mode and the sound should be a bit tighter.
These were some broad generalizations but reasonably accurate when we talk about tube guitar amps with tube rectifiers. Tube rectifiers can be built to over come this sagging sound characteristic but then it wouldn't be as cool to listen to would it?
BTW...when I hit my 666th post, all I got was constipated