How to split single DC powersupply in + and - volts for opamp rails

[TimFox]

it's very hard to split PSU output from unipolar to bipolar, you can't do it without energy loss for transformation.

You can do unipolar to bipolar DC transformation by implementing powerful sine generator powered from unipolar DC, then put that sine into primary coil of the transformer and use two secondary coils with rectifiers to power bipolar regulator.

By using higher frequency you can reduce transformer size and weight. So, it's better to use 400 Hz for transformation instead of usual 50/60 Hz which is used for mains.

If possible, it's better to replace unipolar PSU with bipolar one. It will be much easy, cheaper and more efficient than adding unipolar to bipolar transformation module. If your device is powered from battery, you can add second battery to get bipolar power source.

It's actually very easy to use a rail splitter to obtain bipolar DC voltages from a (floating) unipolar supply.
It will be inefficient if there is a substantial unbalanced load, such as a high current from the output of an op amp powered by the bipolar supply.
In the case I cited of a Wiltron analog phase meter, where there was a string of op amps operating from +/- 15 V, AC coupled from one to the next, where the DC output current of each stage was low, it was a sensible design decision to use a 30 V supply and a simple rail splitter.
If you use a high-frequency generator, you may have to contend with noise from that circuitry.
Again, this is a quantitative question.

[Zero999]

it's very hard to split PSU output from unipolar to bipolar, you can't do it without energy loss for transformation.

You can do unipolar to bipolar DC transformation by implementing powerful sine generator powered from unipolar DC, then put that sine into primary coil of the transformer and use two secondary coils with rectifiers to power bipolar regulator.

By using higher frequency you can reduce transformer size and weight. So, it's better to use 400 Hz for transformation instead of usual 50/60 Hz which is used for mains.

If possible, it's better to replace unipolar PSU with bipolar one. It will be much easy, cheaper and more efficient than adding unipolar to bipolar transformation module. If your device is powered from battery, you can add second battery to get bipolar power source.

It's actually very easy to use a rail splitter to obtain bipolar DC voltages from a (floating) unipolar supply.
It will be inefficient if there is a substantial unbalanced load, such as a high current from the output of an op amp powered by the bipolar supply.
In the case I cited of a Wiltron analog phase meter, where there was a string of op amps operating from +/- 15 V, AC coupled from one to the next, where the DC output current of each stage was low, it was a sensible design decision to use a 30 V supply and a simple rail splitter.
If you use a high-frequency generator, you may have to contend with noise from that circuitry.
Again, this is a quantitative question.

It's possible to do it with high efficiency with a switched mode power supply.

[TimFox]

Or, as one of my German-citizen physics professors replied to a different suggestion:  "You could also pull up your pants with tongs."