Higher voltage is fine…some people say higher capacity is ok as well but I just stick to what was in there and can go
Up on the voltage. I have never had an issue and I have restored a lot of vintage receivers.

Thats fine. If you go up in voltage also look at the cap size, sometimes that can be affected and not fit your footprint. However, most modern caps are much smaller.

I would say it would apply to must general use caps. Similar to diodes and transistors as well. Often you can use higher voltage ratings.

General statements: capacitor voltage is a measure of how much the capacitor can withstand before shorting out. Higher voltage means a more durable though possibly more expensive capacitor. Farad is a measure of the “storage capacity” of the capacitor. Since capacitors are often used in oscillating circuits, having a larger capacitor slows the oscillations as it takes more time for the capacitor to fill. So, changing the farad alters the function of the circuit. In some cases it will work fine in others it will throw things off. Lastly there is the designation as to whether a capacitor is electrolytic. If so, you have to respect the polarity of the capacitor. If they are inserted wrong, it ruins the cell. Ceramic capacitors however don’t have a polarity and can be inserted either way.

Yes, you can definitely go higher on the voltage rating, but the capacitance rating generally needs to be the same.

Radial caps are not hard to find at all. Axials might be tougher to get these days in certain values.

https://www.mouser.com/c/passive-components/capacitors/aluminum-electrolytic-capacitors/aluminum-electrolytic-capacitors-radial-leaded/?q=100uf&capacitance=100%20uF&m=Nichicon~~Panasonic%7C~Vishay%7C~Cornell%20Dubilier&termination%20style=Radial&voltage%20rating%20dc=100%20VDC&instock=y&rp=passive-components%2Fcapacitors%2Faluminum-electrolytic-capacitors%2Faluminum-electrolytic-capacitors-radial-leaded%7C~Manufacturer

It totally depends on the application.
If in a timing circuit like a 555 timer; the capacitance is critical unless it's a bypass cap.
If in a rectifier circuit as a bulk capacitor; then the capacitance is less critical.

As others have stated higher working voltages are generally ok but I wouldn't go much higher than is available. IE if 100V is the rated cap.. if 150 is available. go with that.

If it's like 50uF and you just have a 47uF... that would work.

The other thing to watch for if buying new caps is rated hours vs temperature.
If I am installing new electrolytic in a power supply in a hot chassis (monitor) or near a cpu ... I tend to get 105c (or greater) rated caps with the highest rated hours.

Usually, electrolytic caps work best at about 50% - 75% of the maximum voltage. Using a high voltage cap with much lower voltage will not "form" or create sufficient insulating layer on the capacitor aluminum strips. But here we are talking about using a 400V capacitor at 5 volts or so. It is OK to replace a 100V cap with a 200V one.

For the capacitance value, of course if the capacitor is used as timing element, the replacements capacitance must be the same as original. Usually they are used for filtering DC voltages though, so the capacitance value is not critical. Too much will cause strain in rectifier diodes, because the larger the capacitance, the shorter will be the time when filter capacitor actually charges (only when AC sinewave value is higher than capacitor voltage) and thus the ripple current via diodes to cap will also be higher. Pretty safe to replace a 100 uF cap with a 150 uF or so, though.

And finally, the temperature rating. Many general purpose electrolytics are spec'd at 85 degrees C, while the premium ones are 105 C. In pinball machines, the temperatures are lower even if the caps are near the hot rectifiers. But the higher the temperature, the shorter the capacitor lifetime. A 105 C will last much longer. An electrolytic used near the rated temperature might have a lifetime of only a few thousand hours, while at half the maximum it will last tens of thousands hours. So, always use 105 C electrolytics for replacement.

Electro caps can have a tolerance that varies wildly. It is common for most to have a 20% tolerance. This means your 100uf cap 'could' actually be 80uf or 120uf and still be perfectly within tolerance.

Replacing a 100uf with a 150 would not make any noticable difference in almost all pinball applications.

You do need to take care with the voltage rating however.

To make a logical and informed choice look at where the cap is connected. If it's on a 12V rail then it will likely be a 16~25V rated cap but a 35V or even 50V would work equally well.

Mostly it is common sense - can anyone remember that?