No ever since 1974 FTC rule on how to spec power all amps generally exceed spec by 15-30% all day long. The test was so hard, 1 hour at the most demanding power level (1-3) full frequency and then have the amp had been rode hard it was tested for power.
Thanks for the info guys.
Is that unusual that my amp is putting out 115 watts when it's only rated at 90?
No
Ever since the 1974 law about how power for a stereo amplifier must be specified, all amps generally exceed specification by 15-30%, they all have more power than the number in the spec sheets.
The test required preconditioning, warming up the amp. This was done at 1/3 power the most heat producing power output for a typical solid state power unit back then. The preconditioning was done for 1 hour and the signal amplified was the full frequency response of the rated amp, generally 20Hz-20kHz.
After the preconditioning the now hot amplifier was tested for power output.
Specs must include:
Power in watts RMS not peak or anything else.
Number of channels driven, two for a stereo unit.
The load into which the amplifier was driven, the 4 or 8 ohm speaker for example
Frequency response of the power rating, usually 20-20k but some smaller amps were only rated down to 40Hz so they could have higher number.
The total harmonic distortion limit of the spec.
Because of the difficulty of the test many manufacturers built amps that when not beaten hard before a test would easily exceed the spec number. Additionally, if only one channel is tested the amp will do a bit or a good bit more power than spec.
Your amp is typical.