By 3rd January 2022, if you buy Kenya Power tokens worth ksh. 500, you would get about 31 units
NOTE that tokens vary depending on your usage. If you consume a lot power then you will get less units. For instance, if you use more than 100 units per month for 3 consecutive months then you rates will lowered (you will receive less units as you are considered a high power user).
UPDATE: KPLC has revised its power cost. With ksh. 500, you will now get 31 units (we have updated this answer to reflect the changes).