I also find that the usual "crap" grade of disc ceramic caps tend to run high in value, especially if they have the "Z" tolerance code (which would make sense). These caps are usually used as bulk capacitance (decoupling circuits for example) and value is rarely an issue as long as it has a minimum value limit.
I should post a sticky titled:
"Y5F, Z5U and Why They Are Absolutely Worthless"
The real problem is this:
1) Z5U/Y5F caps
of a given voltage rating/capacitance value are smaller and cheaper than X7R/X5R. So, they are a better buy... right?
WRONG, because the Z5U specs are pure baloney. They only apply at 25C temperature with less than 10% of rated voltage applied to the capacitor. Anythng else and the capacitance vanishes quickly.
EXAMPLE:
A "10uF/10V" Z5U cap is only 10uF as long as you only apply about 1V or less..... as the voltage increases, the capacitance falls off a cliff. In fact,
at the quoted (rated) voltage, Z5U/Y5F capacitance is only about 30% of the spec. So, the spec is pure BS. Of course, you could get a Z5U cap which hold most of it's capacitance at 10V by buying a "50V" Z5U cap... which (what a surprise) is as big and expensive as a 10uF/10V X7R cap.
AS FOR TEMPCO:
Another Z5U/Y5F ripoff. An X7R cap's capacitance will stay within about 20% of quoted spec over the temp range of about -55C to +125C. Pretty good capacitance value.
The tempco on a Z5U looks exactly like an umbrella centered at 25C, dropping about 50% down at the -20C and +80C temp limits. Again, Z5U caps suck.
In reality (if you operate a cap at it's rated voltage and temp range) a Z5U/Y5F will deliver about 10% of rated capacitance. An X7R will probably hold at least 70% or more across all effects (worst case). Bottom line, Z5U/Y5F caps are a scam for people who don't read the specs. In terms of actual capacitance, they don't give more for the money, they give less. They just look smaller/cheaper because the specs are bogus.
See below: X7R tempco left, Z5U tempco second. The capacitance change caused by applied voltage for X7R is shown third, Z5U cap change from applied voltage is at far right (last two curves are both for 50V caps).
Z5U/Y5F caps are totally worthless.