I have a 115VAC primary 24VAC secondary transformer. I thought that if I put 24VAC into the secondary, I'd get 115VAC out. I got 108VAC out:

Ok, that's not too bad, 6% off. But I thought that rectifying would give me 108 x 1.4 = 151VDC. Instead I get 144VDC? I do expect some small amount of drop due to the diodes in the rectifier, but it's at most 2 volts.

The rectifier (KBP206G) is being loaded down with a 22.5k resistor and a 330u 200V capacitor.

I checked the input voltage: 26.7VAC. I removed the resistor: 148VDC. I put the resistor back and used a larger capacitor. 142VDC.

I observed the primary (108VAC) waveform and saw some clipping, which would explain why the reduced DC. I removed the rectifier and the clipping went away. I don't thing this is transformer saturation, since there's no DC across the transformer, and I'm barely pulling any power out of it.

I'm not sure what that's all about. So I ordered a few different transformers, and I'm going to try those to see if it's something systematic that I'm just not understanding.